diff --git a/README.md b/README.md
index 4ba007b..db05791 100644
--- a/README.md
+++ b/README.md
@@ -123,6 +123,7 @@ Requirements: [requests](https://pypi.python.org/pypi/requests)
 
 ```python
 from pixivpy3 import AppPixivAPI
+from pixivpy3 import enums
 
 access_token = "..."
 refresh_token = "..."
@@ -137,7 +138,7 @@ print(f">>> origin url: {illust.image_urls.large}")
 
 # get ranking: 1-30
 # mode: [day, week, month, day_male, day_female, week_original, week_rookie, day_manga]
-json_result = api.illust_ranking('day')
+json_result = api.illust_ranking(mode=enums.RankingMode.DAY)
 for illust in json_result.illusts:
     print(f" p1 [{illust.title}] {illust.image_urls.medium}")
 
@@ -167,6 +168,7 @@ while next_qs:
 
 ```python
 from pixivpy3 import AppPixivAPI
+
 aapi = AppPixivAPI()
 json_result = aapi.illust_ranking()
 for illust in json_result.illusts[:3]:
@@ -179,9 +181,10 @@ for illust in json_result.illusts[:3]:
 2. Change deprecated SPAI call to Public-API call
 
 ```python
-from pixivpy3 import AppPixivAPI
+from pixivpy3 import AppPixivAPI, enums
+
 api = AppPixivAPI()
-rank_list = api.illust_ranking('day')
+rank_list = api.illust_ranking(enums.RankingMode.DAY)
 print(rank_list)
 
 # more fields about response: https://github.com/upbit/pixivpy/wiki/sniffer
@@ -208,8 +211,8 @@ Find Pixiv API in **Objective-C**? You might also like
 ```python
 from __future__ import annotations
 from typing import Any
+from pixivpy3 import enums
 from pixivpy3.utils import ParsedJson
-
 from pixivpy3.api import BasePixivAPI
 
 
@@ -223,20 +226,20 @@ class AppPixivAPI(BasePixivAPI):
 
     # 用户作品列表
     ## type: [illust, manga]
-    def user_illusts(self, user_id: int | str, type="illust") -> ParsedJson: ...
+    def user_illusts(self, user_id: int | str, type=enums.ContentType.ILLUSTRATION) -> ParsedJson: ...
 
     # 用户收藏作品列表
     # tag: 从 user_bookmark_tags_illust 获取的收藏标签
-    def user_bookmarks_illust(self, user_id: int | str, restrict="public") -> ParsedJson: ...
+    def user_bookmarks_illust(self, user_id: int | str, restrict=enums.Visibility.PUBLIC) -> ParsedJson: ...
 
     # 用户收藏作品列表中的小说
-    def user_bookmarks_novel(self, user_id: int | str, restrict="public") -> ParsedJson: ...
+    def user_bookmarks_novel(self, user_id: int | str, restrict=enums.Visibility.PUBLIC) -> ParsedJson: ...
 
     def user_related(self, seed_user_id: int | str) -> ParsedJson: ...
 
     # 关注用户的新作
     # restrict: [public, private]
-    def illust_follow(self, restrict="public") -> ParsedJson: ...
+    def illust_follow(self, restrict=enums.Visibility.PUBLIC) -> ParsedJson: ...
 
     # 作品详情 (类似PAPI.works(),iOS中未使用)
     def illust_detail(self, illust_id: int | str) -> ParsedJson: ...
@@ -249,7 +252,7 @@ class AppPixivAPI(BasePixivAPI):
 
     # 插画推荐 (Home - Main)
     # content_type: [illust, manga]
-    def illust_recommended(self, content_type="illust") -> ParsedJson: ...
+    def illust_recommended(self, content_type=enums.ContentType.ILLUSTRATION) -> ParsedJson: ...
 
     # 小说推荐
     def novel_recommended(self) -> ParsedJson: ...
@@ -259,7 +262,7 @@ class AppPixivAPI(BasePixivAPI):
     # date: '2016-08-01'
     # mode (Past): [day, week, month, day_male, day_female, week_original, week_rookie,
     #               day_r18, day_male_r18, day_female_r18, week_r18, week_r18g]
-    def illust_ranking(self, mode="day", date=None) -> ParsedJson: ...
+    def illust_ranking(self, mode=enums.RankingMode.DAY, date=None) -> ParsedJson: ...
 
     # 趋势标签 (Search - tags)
     def trending_tags_illust(self) -> ParsedJson: ...
@@ -273,13 +276,13 @@ class AppPixivAPI(BasePixivAPI):
     # duration: [within_last_day, within_last_week, within_last_month]
     # start_date, end_date: '2020-07-01'
     def search_illust(
-            self,
-            word: str,
-            search_target="partial_match_for_tags",
-            sort="date_desc",
-            duration=None,
-            start_date=None,
-            end_date=None,
+        self,
+        word: str,
+        search_target=enums.SearchTarget.PARTIAL_MATCH_FOR_TAGS,
+        sort=enums.Sort.DATE_DESC,
+        duration=None,
+        start_date=None,
+        end_date=None,
     ) -> ParsedJson: ...
 
     # 搜索小说 (Search Novel)
@@ -291,36 +294,36 @@ class AppPixivAPI(BasePixivAPI):
     # sort: [date_desc, date_asc]
     # start_date/end_date: 2020-06-01
     def search_novel(
-            self,
-            word: str,
-            search_target="partial_match_for_tags",
-            sort="date_desc",
-            start_date=None,
-            end_date=None,
+        self,
+        word: str,
+        search_target=enums.SearchTarget.PARTIAL_MATCH_FOR_TAGS,
+        sort=enums.Sort.DATE_DESC,
+        start_date=None,
+        end_date=None,
     ) -> ParsedJson: ...
 
-    def search_user(self, word: str, sort='date_desc', duration=None) -> ParsedJson: ...
+    def search_user(self, word: str, sort=enums.Sort.DATE_DESC, duration=None) -> ParsedJson: ...
 
     # 作品收藏详情
     def illust_bookmark_detail(self, illust_id: int | str) -> ParsedJson: ...
 
     # 新增收藏
-    def illust_bookmark_add(self, illust_id: int | str, restrict="public", tags=None) -> ParsedJson: ...
+    def illust_bookmark_add(self, illust_id: int | str, restrict=enums.Visibility.PUBLIC, tags=None) -> ParsedJson: ...
 
     # 删除收藏
     def illust_bookmark_delete(self, illust_id: int | str) -> ParsedJson: ...
 
     # 关注用户
-    def user_follow_add(self, user_id: int | str, restrict="public") -> ParsedJson: ...
+    def user_follow_add(self, user_id: int | str, restrict=enums.Visibility.PUBLIC) -> ParsedJson: ...
 
     # 取消关注用户
     def user_follow_delete(self, user_id: int | str) -> ParsedJson: ...
 
     # 用户收藏标签列表
-    def user_bookmark_tags_illust(self, restrict="public") -> ParsedJson: ...
+    def user_bookmark_tags_illust(self, restrict=enums.Visibility.PUBLIC) -> ParsedJson: ...
 
     # Following用户列表
-    def user_following(self, user_id: int | str, restrict="public") -> ParsedJson: ...
+    def user_following(self, user_id: int | str, restrict=enums.Visibility.PUBLIC) -> ParsedJson: ...
 
     # Followers用户列表
     def user_follower(self, user_id: int | str) -> ParsedJson: ...
@@ -351,7 +354,7 @@ class AppPixivAPI(BasePixivAPI):
 
     # 大家的新作
     # content_type: [illust, manga]
-    def illust_new(self, content_type="illust", max_illust_id=None) -> ParsedJson: ...
+    def illust_new(self, content_type=enums.ContentType.ILLUSTRATION, max_illust_id=None) -> ParsedJson: ...
 
     def novel_new(self, max_novel_id=None) -> ParsedJson: ...
 
@@ -362,7 +365,8 @@ class AppPixivAPI(BasePixivAPI):
 [Usage](https://github.com/upbit/pixivpy/blob/aec177aa7a1979f7ec4c5bbbeed9085cc256bdbd/demo.py#L306):
 
 ```python
-from pixivpy3 import AppPixivAPI
+from pixivpy3 import AppPixivAPI, enums
+
 api = AppPixivAPI()
 
 # 作品推荐
@@ -409,7 +413,7 @@ novel = json_result.novels[0]
 print(f">>> {novel.title}, text_length: {novel.text_length}, series: {novel.series}")
 
 # 2016-07-15 日的过去一周排行
-json_result = api.illust_ranking('week', date='2016-07-15')
+json_result = api.illust_ranking(enums.RankingMode.WEEK, date='2016-07-15')
 print(json_result)
 illust = json_result.illusts[0]
 print(f">>> {illust.title}, origin url: {illust.image_urls.large}")
@@ -421,7 +425,7 @@ illust = json_result.illusts[0]
 print(f">>> {illust.title}, origin url: {illust.image_urls.large}")
 
 # 标签 "水着" 搜索
-json_result = api.search_illust('水着', search_target='partial_match_for_tags')
+json_result = api.search_illust('水着', search_target=enums.SearchTarget.PARTIAL_MATCH_FOR_TAGS)
 print(json_result)
 illust = json_result.illusts[0]
 print(f">>> {illust.title}, origin url: {illust.image_urls.large}")
@@ -437,9 +441,11 @@ json_result = api.novel_comments(16509454, include_total_comments=True)
 print(f"Total comments = {json_result.total_comments}")
 for comment in json_result.comments:
     if comment.parent_comment:
-        print(f"{comment.user.name} replied to {comment.parent_comment.user.name} at {comment.date} : {comment.comment}")
+        text = f"{comment.user.name} replied to {comment.parent_comment.user.name} at {comment.date} : {comment.comment}"
+        print(text)
     else:
-        print(f"{comment.user.name} at {comment.date} : {comment.comment}")
+        text = f"{comment.user.name} at {comment.date} : {comment.comment}"
+        print(text)
 ```
 
 ## Develop Instructions
diff --git a/demo.py b/demo.py
index e63fb5d..827f150 100644
--- a/demo.py
+++ b/demo.py
@@ -5,7 +5,7 @@
 import time
 from typing import Any
 
-from pixivpy3 import AppPixivAPI, PixivError
+from pixivpy3 import AppPixivAPI, PixivError, enums
 
 sys.dont_write_bytecode = True
 
@@ -135,7 +135,9 @@ def appapi_search(aapi: AppPixivAPI) -> None:
             first_tag = trend_tag.tag
         print(f"{trend_tag.tag} -  {trend_tag.illust.title}(id={trend_tag.illust.id})")
 
-    json_result = aapi.search_illust(first_tag, search_target="partial_match_for_tags")
+    json_result = aapi.search_illust(
+        first_tag, search_target=enums.SearchTarget.PARTIAL_MATCH_FOR_TAGS
+    )
     print(json_result)
     illust = json_result.illusts[0]
     print(f">>> {illust.title}, origin url: {illust.image_urls.large}")
@@ -149,7 +151,7 @@ def appapi_search(aapi: AppPixivAPI) -> None:
         print(f">>> {illust.title}, origin url: {illust.image_urls.large}")
 
     # novel
-    json_result = aapi.search_novel("FGO", search_target="keyword")
+    json_result = aapi.search_novel("FGO", search_target=enums.SearchTarget.KEYWORD)
     print(json_result)
     novel = json_result.novels[0]
     print(f">>> {illust.title}, origin url: {illust.image_urls.large}")
@@ -163,10 +165,12 @@ def appapi_search(aapi: AppPixivAPI) -> None:
         print(f">>> {novel.title}, origin url: {novel.image_urls['large']}")
 
     json_result = aapi.search_illust(
-        "AI生成", search_target="exact_match_for_tags", search_ai_type=0
+        "AI生成",
+        search_target=enums.SearchTarget.EXACT_MATCH_FOR_TAGS,
+        search_ai_type=0,
     )
-    # 关闭AI搜索选项后,将过滤掉所有illust_ai_type=2的插画,而illust_ai_type=1 or 0 的插画将被保留
-    # 但是,加入了"AI生成"的tag却没有在作品提交时打开“AI生成”的开关的作品不会被筛选出结果列表
+    # 关闭AI搜索选项后，将过滤掉所有illust_ai_type=2的插画，而illust_ai_type=1 or 0 的插画将被保留
+    # 但是，加入了"AI生成"的tag却没有在作品提交时打开“AI生成”的开关的作品不会被筛选出结果列表
     print(json_result.illusts[0])
 
 
diff --git a/download_illusts.py b/download_illusts.py
index 2a0c2a5..eccc160 100644
--- a/download_illusts.py
+++ b/download_illusts.py
@@ -3,7 +3,7 @@
 import os
 import sys
 
-from pixivpy3 import AppPixivAPI, ByPassSniApi
+from pixivpy3 import AppPixivAPI, ByPassSniApi, enums
 
 sys.dont_write_bytecode = True
 
@@ -23,7 +23,7 @@ def main() -> None:
     api.auth(refresh_token=_REFRESH_TOKEN)
 
     # get rankings
-    json_result = api.illust_ranking("day", date="2019-01-01")
+    json_result = api.illust_ranking(enums.RankingMode.DAY, date="2019-01-01")
 
     directory = "illusts"
     if not os.path.exists(directory):
diff --git a/example_bypass_sni.py b/example_bypass_sni.py
index 8ad8ad6..e22b907 100644
--- a/example_bypass_sni.py
+++ b/example_bypass_sni.py
@@ -1,7 +1,7 @@
 import sys
 from datetime import datetime, timedelta
 
-from pixivpy3 import ByPassSniApi
+from pixivpy3 import ByPassSniApi, enums
 
 sys.dont_write_bytecode = True
 
@@ -20,7 +20,7 @@ def main() -> None:
     # api.login(_USERNAME, _PASSWORD)
     print(api.auth(refresh_token=_REFRESH_TOKEN))
     date = datetime.now() - timedelta(days=5)
-    json_result = api.illust_ranking("day", date=date)
+    json_result = api.illust_ranking(enums.RankingMode.DAY, date=date)
 
     print(
         "Printing image titles and tags with English tag translations present when available"
diff --git a/example_tag_translations.py b/example_tag_translations.py
index 8c6c65f..87ca5ed 100644
--- a/example_tag_translations.py
+++ b/example_tag_translations.py
@@ -3,7 +3,7 @@
 import sys
 from datetime import datetime, timedelta
 
-from pixivpy3 import AppPixivAPI
+from pixivpy3 import AppPixivAPI, enums
 
 sys.dont_write_bytecode = True
 
@@ -20,7 +20,7 @@ def main() -> None:
 
     aapi.auth(refresh_token=_REFRESH_TOKEN)
     date = datetime.now() - timedelta(days=5)
-    json_result = aapi.illust_ranking("day", date=date)
+    json_result = aapi.illust_ranking(enums.RankingMode.DAY, date=date)
 
     print(
         "Printing image titles and tags with English tag translations present when available"
diff --git a/pixivpy3/aapi.py b/pixivpy3/aapi.py
index f6ffd24..feccdd8 100644
--- a/pixivpy3/aapi.py
+++ b/pixivpy3/aapi.py
@@ -8,50 +8,24 @@
 import datetime as dt
 import re
 import urllib.parse as up
-from typing import Any, Literal, Union
-
-try:
-    # Python>=3.10
-    from typing import TypeAlias
-except ImportError:
-    from typing_extensions import TypeAlias
+from typing import Any, Literal, TypeVar, Union
 
+from pydantic import BaseModel
 from requests.structures import CaseInsensitiveDict
+from typing_extensions import TypeAlias  # present in `typing` only from `3.10`
 
-from . import models
+from . import enums, models
 from .api import BasePixivAPI
-from .models import ModelT
 from .utils import ParamDict, ParsedJson, PixivError, Response
 
 # from typeguard import typechecked
-_FILTER: TypeAlias = Literal["for_ios", ""]
-_TYPE: TypeAlias = Literal["illust", "manga", ""]
-_RESTRICT: TypeAlias = Literal["public", "private", ""]
-_CONTENT_TYPE: TypeAlias = Literal["illust", "manga", ""]
-_MODE: TypeAlias = Literal[
-    "day",
-    "week",
-    "month",
-    "day_male",
-    "day_female",
-    "week_original",
-    "week_rookie",
-    "day_manga",
-    "day_r18",
-    "day_male_r18",
-    "day_female_r18",
-    "week_r18",
-    "week_r18g",
-    "",
-]
-_SEARCH_TARGET: TypeAlias = Literal[
-    "partial_match_for_tags", "exact_match_for_tags", "title_and_caption", "keyword", ""
-]
-_SORT: TypeAlias = Literal["date_desc", "date_asc", "popular_desc", ""]
-_DURATION: TypeAlias = Literal[
-    "within_last_day", "within_last_week", "within_last_month", "", None
-]
-_BOOL: TypeAlias = Literal["true", "false"]
+__all__ = ("AppPixivAPI",)
+
+ModelT = TypeVar("ModelT", bound=BaseModel)
+
+BoolStr: TypeAlias = Literal["true", "false"]
+Filter: TypeAlias = Literal["for_ios"]
+FILTER = "for_ios"
 
 DateOrStr = Union[dt.date, str]
 
@@ -119,7 +93,7 @@ def _load_model(cls, data: ParsedJson, model: type[ModelT], /) -> ModelT:
             raise PixivError(msg, body=data) from e
 
     @classmethod
-    def format_bool(cls, bool_value: bool | str | None) -> _BOOL:
+    def format_bool(cls, bool_value: bool | str | None) -> BoolStr:
         if isinstance(bool_value, bool):
             return "true" if bool_value else "false"
         if bool_value in {"true", "True"}:
@@ -157,7 +131,7 @@ def parse_qs(cls, next_url: str | None) -> dict[str, Any] | None:
     def user_detail(
         self,
         user_id: int | str,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         req_auth: bool = True,
     ) -> models.UserInfoDetailed:
         url = f"{self.hosts}/v1/user/detail"
@@ -173,8 +147,8 @@ def user_detail(
     def user_illusts(
         self,
         user_id: int | str,
-        type: _TYPE = "illust",
-        filter: _FILTER = "for_ios",
+        type: enums.ContentType = enums.ContentType.ILLUSTRATION,
+        filter: Filter = FILTER,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> models.UserIllustrations:
@@ -195,8 +169,8 @@ def user_illusts(
     def user_bookmarks_illust(
         self,
         user_id: int | str,
-        restrict: _RESTRICT = "public",
-        filter: _FILTER = "for_ios",
+        restrict: enums.Visibility = enums.Visibility.PUBLIC,
+        filter: Filter = FILTER,
         max_bookmark_id: int | str | None = None,
         tag: str | None = None,
         req_auth: bool = True,
@@ -218,8 +192,8 @@ def user_bookmarks_illust(
     def user_bookmarks_novel(
         self,
         user_id: int | str,
-        restrict: _RESTRICT = "public",
-        filter: _FILTER = "for_ios",
+        restrict: enums.Visibility = enums.Visibility.PUBLIC,
+        filter: Filter = FILTER,
         max_bookmark_id: int | str | None = None,
         tag: str | None = None,
         req_auth: bool = True,
@@ -240,7 +214,7 @@ def user_bookmarks_novel(
     def user_related(
         self,
         seed_user_id: int | str,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -256,7 +230,7 @@ def user_related(
 
     def user_recommended(
         self,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -274,7 +248,7 @@ def user_recommended(
     # restrict: [public, private]
     def illust_follow(
         self,
-        restrict: _RESTRICT = "public",
+        restrict: enums.Visibility = enums.Visibility.PUBLIC,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -319,7 +293,7 @@ def illust_comments(
     def illust_related(
         self,
         illust_id: int | str,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         seed_illust_ids: int | str | list[str] | None = None,
         offset: int | str | None = None,
         viewed: str | list[str] | None = None,
@@ -346,9 +320,9 @@ def illust_related(
     # content_type: [illust, manga]
     def illust_recommended(
         self,
-        content_type: _CONTENT_TYPE = "illust",
+        content_type: enums.ContentType = enums.ContentType.ILLUSTRATION,
         include_ranking_label: bool | str = True,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         max_bookmark_id_for_recommend: int | str | None = None,
         min_bookmark_id_for_recent_illust: int | str | None = None,
         offset: int | str | None = None,
@@ -420,7 +394,7 @@ def novel_comments(
     def novel_recommended(
         self,
         include_ranking_label: bool | str = True,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         offset: int | str | None = None,
         include_ranking_novels: str | bool | None = None,
         already_recommended: str | list[str] | None = None,
@@ -459,8 +433,8 @@ def novel_recommended(
     #               day_r18, day_male_r18, day_female_r18, week_r18, week_r18g]
     def illust_ranking(
         self,
-        mode: _MODE = "day",
-        filter: _FILTER = "for_ios",
+        mode: enums.RankingMode = enums.RankingMode.DAY,
+        filter: Filter = FILTER,
         date: DateOrStr | None = None,
         offset: int | str | None = None,
         req_auth: bool = True,
@@ -479,9 +453,9 @@ def illust_ranking(
 
     # 趋势标签 (Search - tags)
     def trending_tags_illust(
-        self, filter: _FILTER = "for_ios", req_auth: bool = True
+        self, filter: Filter = FILTER, req_auth: bool = True
     ) -> ParsedJson:
-        url = f"{self.hosts}/v1/trending-tags/illust"
+        url = "%s/v1/trending-tags/illust" % self.hosts
         params = {
             "filter": filter,
         }
@@ -500,12 +474,12 @@ def trending_tags_illust(
     def search_illust(
         self,
         word: str,
-        search_target: _SEARCH_TARGET = "partial_match_for_tags",
-        sort: _SORT = "date_desc",
-        duration: _DURATION = None,
+        search_target: enums.SearchTarget = enums.SearchTarget.PARTIAL_MATCH_FOR_TAGS,
+        sort: enums.Sort = enums.Sort.DATE_DESC,
+        duration: enums.Duration | None = None,
         start_date: DateOrStr | None = None,
         end_date: DateOrStr | None = None,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         search_ai_type: Literal[0, 1] | None = None,
         offset: int | str | None = None,
         req_auth: bool = True,
@@ -542,10 +516,10 @@ def search_illust(
     def search_novel(
         self,
         word: str,
-        search_target: _SEARCH_TARGET = "partial_match_for_tags",
-        sort: _SORT = "date_desc",
-        merge_plain_keyword_results: _BOOL = "true",
-        include_translated_tag_results: _BOOL = "true",
+        search_target: enums.SearchTarget = enums.SearchTarget.PARTIAL_MATCH_FOR_TAGS,
+        sort: enums.Sort = enums.Sort.DATE_DESC,
+        merge_plain_keyword_results: BoolStr = "true",
+        include_translated_tag_results: BoolStr = "true",
         start_date: DateOrStr | None = None,
         end_date: DateOrStr | None = None,
         filter: str | None = None,
@@ -576,9 +550,9 @@ def search_novel(
     def search_user(
         self,
         word: str,
-        sort: _SORT = "date_desc",
-        duration: _DURATION = None,
-        filter: _FILTER = "for_ios",
+        sort: enums.Sort = enums.Sort.DATE_DESC,
+        duration: enums.Duration | None = None,
+        filter: Filter = FILTER,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -610,7 +584,7 @@ def illust_bookmark_detail(
     def illust_bookmark_add(
         self,
         illust_id: int | str,
-        restrict: _RESTRICT = "public",
+        restrict: enums.Visibility = enums.Visibility.PUBLIC,
         tags: str | list[str] | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -642,7 +616,7 @@ def illust_bookmark_delete(
     def user_follow_add(
         self,
         user_id: int | str,
-        restrict: _RESTRICT = "public",
+        restrict: enums.Visibility = enums.Visibility.PUBLIC,
         req_auth: bool = True,
     ) -> ParsedJson:
         url = f"{self.hosts}/v1/user/follow/add"
@@ -661,7 +635,7 @@ def user_follow_delete(
 
     # 设置用户选项中是否展现AI生成作品
     def user_edit_ai_show_settings(
-        self, setting: _BOOL, req_auth: bool = True
+        self, setting: BoolStr, req_auth: bool = True
     ) -> ParsedJson:
         url = f"{self.hosts}/v1/user/ai-show-settings/edit"
         data = {"show_ai": setting}
@@ -672,7 +646,7 @@ def user_edit_ai_show_settings(
     def user_bookmark_tags_illust(
         self,
         user_id: int | str,
-        restrict: _RESTRICT = "public",
+        restrict: enums.Visibility = enums.Visibility.PUBLIC,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -690,7 +664,7 @@ def user_bookmark_tags_illust(
     def user_following(
         self,
         user_id: int | str,
-        restrict: _RESTRICT = "public",
+        restrict: enums.Visibility = enums.Visibility.PUBLIC,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> models.UserFollowing:
@@ -709,7 +683,7 @@ def user_following(
     def user_follower(
         self,
         user_id: int | str,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -745,7 +719,7 @@ def user_mypixiv(
     def user_list(
         self,
         user_id: int | str,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -776,7 +750,7 @@ def ugoira_metadata(
     def user_novels(
         self,
         user_id: int | str,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         offset: int | str | None = None,
         req_auth: bool = True,
     ) -> models.UserNovels:
@@ -794,7 +768,7 @@ def user_novels(
     def novel_series(
         self,
         series_id: int | str,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         last_order: str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -825,7 +799,7 @@ def novel_detail(
 
     def novel_new(
         self,
-        filter: _FILTER = "for_ios",
+        filter: Filter = FILTER,
         max_novel_id: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -842,7 +816,7 @@ def novel_new(
     # restrict: [public, private, all]
     def novel_follow(
         self,
-        restrict: _RESTRICT = "public",
+        restrict: enums.Visibility = enums.Visibility.PUBLIC,
         offset: int | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
@@ -894,8 +868,8 @@ def novel_text(
     # content_type: [illust, manga]
     def illust_new(
         self,
-        content_type: _CONTENT_TYPE = "illust",
-        filter: _FILTER = "for_ios",
+        content_type: enums.ContentType = enums.ContentType.ILLUSTRATION,
+        filter: Filter = FILTER,
         max_illust_id: int | str | None = None,
         req_auth: bool = True,
     ) -> ParsedJson:
diff --git a/pixivpy3/enums.py b/pixivpy3/enums.py
new file mode 100644
index 0000000..eccffeb
--- /dev/null
+++ b/pixivpy3/enums.py
@@ -0,0 +1,55 @@
+from enum import Enum
+
+__all__ = (
+    "ContentType",
+    "Visibility",
+    "RankingMode",
+    "SearchTarget",
+    "Sort",
+    "Duration",
+)
+
+
+class ContentType(str, Enum):
+    ILLUSTRATION = "illust"
+    MANGA = "manga"
+
+
+class Visibility(str, Enum):
+    PUBLIC = "public"
+    PRIVATE = "private"
+
+
+class RankingMode(str, Enum):
+    DAY = "day"
+    WEEK = "week"
+    MONTH = "month"
+    DAY_MALE = "day_male"
+    DAY_FEMALE = "day_female"
+    WEEK_ORIGINAL = "week_original"
+    WEEK_ROOKIE = "week_rookie"
+    DAY_MANGA = "day_manga"
+    DAY_R18 = "day_r18"
+    DAY_MALE_R18 = "day_male_r18"
+    DAY_FEMALE_R18 = "day_female_r18"
+    WEEK_R18 = "week_r18"
+    WEEK_R18G = "week_r18g"
+
+
+class SearchTarget(str, Enum):
+    PARTIAL_MATCH_FOR_TAGS = "partial_match_for_tags"
+    EXACT_MATCH_FOR_TAGS = "exact_match_for_tags"
+    TITLE_AND_CAPTION = "title_and_caption"
+    KEYWORD = "keyword"
+
+
+class Sort(str, Enum):
+    DATE_DESC = "date_desc"
+    DATE_ASC = "date_asc"
+    POPULAR_DESC = "popular_desc"
+
+
+class Duration(str, Enum):
+    WITHIN_LAST_DAY = "within_last_day"
+    WITHIN_LAST_WEEK = "within_last_week"
+    WITHIN_LAST_MONTH = "within_last_month"
diff --git a/pixivpy3/models.py b/pixivpy3/models.py
index fa9a950..c7c15c0 100644
--- a/pixivpy3/models.py
+++ b/pixivpy3/models.py
@@ -1,4 +1,4 @@
-from typing import Any, List, Optional, TypeVar, Union
+from typing import Any, List, Optional, Union
 
 import pydantic
 from typing_extensions import Self
@@ -70,8 +70,6 @@ def _to_camel(string: str) -> str:
     msg = f"Unsupported Pydantic version: {pydantic.__version__}"
     raise ValueError(msg)
 
-ModelT = TypeVar("ModelT", bound=BaseModel)
-
 
 class BasePixivpyModel(BaseModel):
     if _PYDANTIC_MAJOR_VERSION == 2: