diff --git a/src/narou-search-results.ts b/src/narou-search-results.ts
index 4b58aa0..ad0c195 100644
--- a/src/narou-search-results.ts
+++ b/src/narou-search-results.ts
@@ -187,7 +187,7 @@ export interface UserSearchResult {
    * ユーザ名のフリガナの頭文字
    * ひらがな以外の場合はnullまたは空文字となります。
    */
-  name1st: string;
+  name1st: string | null;
   /** 小説投稿数 */
   novel_cnt: number;
   /** レビュー投稿数 */
diff --git a/src/params.ts b/src/params.ts
index f8d77da..94d0284 100644
--- a/src/params.ts
+++ b/src/params.ts
@@ -248,8 +248,6 @@ export const R18Fields = {
   title: "t",
   /** Nコード */
   ncode: "n",
-  /** 作者のユーザID(数値) */
-  userid: "u",
   /** 作者名 */
   writer: "w",
   /** 小説のあらすじ */
@@ -321,7 +319,7 @@ export const R18Fields = {
 
 export type R18Fields = (typeof R18Fields)[keyof Omit<
   NarouSearchResult,
-  "novel_type" | "weekly_unique" | "biggenre" | "genre" | "isr15"
+  "novel_type" | "weekly_unique" | "biggenre" | "genre" | "isr15" | "userid"
 >];
 
 /**
diff --git a/src/search-builder-r18.ts b/src/search-builder-r18.ts
index ce24840..8f18562 100644
--- a/src/search-builder-r18.ts
+++ b/src/search-builder-r18.ts
@@ -15,7 +15,7 @@ import type {
 
 export type DefaultR18SearchResultFields = keyof Omit<
   NarouSearchResult,
-  "weekly_unique" | "noveltype" | "biggenre" | "genre" | "isr15" | "id"
+  "weekly_unique" | "noveltype" | "biggenre" | "genre" | "isr15" | "userid"
 >;
 
 /**
diff --git a/src/search-builder.ts b/src/search-builder.ts
index 9b66f31..b4c5d32 100644
--- a/src/search-builder.ts
+++ b/src/search-builder.ts
@@ -161,6 +161,10 @@ export abstract class SearchBuilderBase<
   }
 }
 
+/**
+ * 要素の抽出条件と除外条件は独立して保持します。
+ * 同じ条件にtrueとfalseを指定すると両方をAPIへ送信し、検索結果は0件になります。
+ */
 export abstract class NovelSearchBuilderBase<
   T extends SearchResultFieldNames,
 > extends SearchBuilderBase<SearchParams, Order> {
diff --git a/test/builder-types.test.ts b/test/builder-types.test.ts
index bd4f67a..0672b9a 100644
--- a/test/builder-types.test.ts
+++ b/test/builder-types.test.ts
@@ -70,6 +70,35 @@ describe.each([
     >().toEqualTypeOf<readonly { noveltype: 1 | 2 }[]>();
   });
 
+  test("R18検索はuseridを取得項目に含めない", () => {
+    const r18 = api.searchR18();
+    const novel = api.search();
+    expectTypeOf<
+      Awaited<ReturnType<typeof r18.execute>>["values"][number]
+    >().not.toHaveProperty("userid");
+    expectTypeOf<
+      Awaited<ReturnType<typeof novel.execute>>["values"][number]
+    >().toHaveProperty("userid").toEqualTypeOf<number>();
+    expectTypeOf(R18Fields).not.toHaveProperty("userid");
+
+    function invalidUsage() {
+      // @ts-expect-error R18 APIはユーザーIDの出力に対応していない
+      api.searchR18().fields(Fields.userid);
+    }
+    expectTypeOf(invalidUsage).returns.toBeVoid();
+  });
+
+  test("ユーザーのname1stはnullを許容する", () => {
+    const all = api.searchUser();
+    const selected = api.searchUser().fields(UserFields.name1st);
+    expectTypeOf<
+      Awaited<ReturnType<typeof all.execute>>["values"][number]["name1st"]
+    >().toEqualTypeOf<string | null>();
+    expectTypeOf<
+      Awaited<ReturnType<typeof selected.execute>>["values"]
+    >().toEqualTypeOf<readonly { name1st: string | null }[]>();
+  });
+
   test("通常検索のoptとfieldsの順序に依存しない型推論", () => {
     const optFirst = api
       .search()
diff --git a/test/narou-search-results.test.ts b/test/narou-search-results.test.ts
index 2888d08..1a381dc 100644
--- a/test/narou-search-results.test.ts
+++ b/test/narou-search-results.test.ts
@@ -49,6 +49,14 @@ describe('NarouSearchResults', () => {
     expect(results.values).toEqual(data);
   });
 
+  it('開始位置がページ境界でなくても従来の計算を維持する', () => {
+    const results = new NarouSearchResults<MockData, 'id'>(
+      [{ allcount: 100 }], { st: 21, lim: 20 }
+    );
+    expect(results.start).toBe(21);
+    expect(results.page).toBe(1.05);
+  });
+
   it('should handle empty results', () => {
     const header = { allcount: 0 };
     const data: Pick<MockData, 'id'>[] = [];
diff --git a/test/search-builder-r18.test.ts b/test/search-builder-r18.test.ts
index 139f332..1859584 100644
--- a/test/search-builder-r18.test.ts
+++ b/test/search-builder-r18.test.ts
@@ -56,6 +56,52 @@ describe("SearchBuilderR18", () => {
   afterEach(() => server.resetHandlers());
   afterAll(() => server.close());
 
+  describe("抽出・除外条件の併存", () => {
+    test.each([
+      ["isBL", "isbl", "notbl"],
+      ["isGL", "isgl", "notgl"],
+      ["isZankoku", "iszankoku", "notzankoku"],
+      ["isTensei", "istensei", "nottensei"],
+      ["isTenni", "istenni", "nottenni"],
+    ] as const)(
+      "%sの両条件を呼び出し順に関係なく保持する",
+      async (method, include, exclude) => {
+        const queries: URLSearchParams[] = [];
+        server.use(
+          http.get(`https://api.syosetu.com/novel18api/api/`, ({ request }) => {
+            queries.push(new URL(request.url).searchParams);
+            return responseGzipOrJson([{ allcount: 0 }], new URL(request.url));
+          })
+        );
+        for (const first of [true, false]) {
+          const result = await NarouAPI.searchR18()
+            .gzip(0)
+            [method](first)
+            [method](!first)
+            .execute();
+          expect(result.allcount).toBe(0);
+          expect(result.values).toEqual([]);
+        }
+        expect(queries).toHaveLength(2);
+        for (const query of queries) {
+          expect(query.get(include)).toBe("1");
+          expect(query.get(exclude)).toBe("1");
+        }
+      }
+    );
+  });
+
+  describe("page", () => {
+    test.each([0, 1, 2])("page=%iの従来の開始位置を維持する", async (page) => {
+      const mockFn = vi.fn();
+      setupMockHandler(mockFn, ["st", "lim"], { ncode: "N1234AB" });
+      const result = await NarouAPI.searchR18().page(page, 20).execute();
+      expect(mockFn).toHaveBeenCalledWith(String(page * 20), "20", 4);
+      expect(result.start).toBe(page * 20);
+      expect(result.page).toBe(page);
+    });
+  });
+
   describe("execute", () => {
     test("execute should call executeNovel18", async () => {
       const mockFn = vi.fn();
diff --git a/test/search-builder.test.ts b/test/search-builder.test.ts
index 63423c7..fc85de3 100644
--- a/test/search-builder.test.ts
+++ b/test/search-builder.test.ts
@@ -60,6 +60,41 @@ describe("SearchBuilder", () => {
   afterEach(() => server.resetHandlers());
   afterAll(() => server.close());
 
+  describe("抽出・除外条件の併存", () => {
+    test.each([
+      ["isBL", "isbl", "notbl"],
+      ["isGL", "isgl", "notgl"],
+      ["isZankoku", "iszankoku", "notzankoku"],
+      ["isTensei", "istensei", "nottensei"],
+      ["isTenni", "istenni", "nottenni"],
+    ] as const)(
+      "%sの両条件を呼び出し順に関係なく保持する",
+      async (method, include, exclude) => {
+        const queries: URLSearchParams[] = [];
+        server.use(
+          http.get(`https://api.syosetu.com/novelapi/api/`, ({ request }) => {
+            queries.push(new URL(request.url).searchParams);
+            return responseGzipOrJson([{ allcount: 0 }], new URL(request.url));
+          })
+        );
+        for (const first of [true, false]) {
+          const result = await NarouAPI.search()
+            .gzip(0)
+            [method](first)
+            [method](!first)
+            .execute();
+          expect(result.allcount).toBe(0);
+          expect(result.values).toEqual([]);
+        }
+        expect(queries).toHaveLength(2);
+        for (const query of queries) {
+          expect(query.get(include)).toBe("1");
+          expect(query.get(exclude)).toBe("1");
+        }
+      }
+    );
+  });
+
   describe("gzip", () => {
     test("default", async () => {
       const mockFn = vi.fn();
@@ -176,11 +211,13 @@ describe("SearchBuilder", () => {
 
   describe("page", () => {
     describe("default count", () => {
-      test.each([1, 2, 3, 4, 5] as const)("if page = %i", async (page) => {
+      test.each([0, 1, 2, 3, 4, 5] as const)("if page = %i", async (page) => {
         const mockFn = vi.fn();
         setupMockHandler(mockFn, ["lim", "st", "gzip", "out"]);
 
         const result = await NarouAPI.search().page(page).execute();
+        expect(result.start).toBe(page * 20);
+        expect(result.page).toBe(page);
         expect(result.allcount).toBe(1);
         expect(result.length).toBe(1);
         expect(result.values).toHaveLength(1);
@@ -197,11 +234,13 @@ describe("SearchBuilder", () => {
     });
 
     describe.each([1, 10, 100, 500] as const)("if count = %i", (count) => {
-      test.each([1, 2, 3, 4, 5] as const)("if page = %i", async (page) => {
+      test.each([0, 1, 2, 3, 4, 5] as const)("if page = %i", async (page) => {
         const mockFn = vi.fn();
         setupMockHandler(mockFn, ["lim", "st", "gzip", "out"]);
 
         const result = await NarouAPI.search().page(page, count).execute();
+        expect(result.start).toBe(page * count);
+        expect(result.page).toBe(page);
         expect(result.allcount).toBe(1);
         expect(result.length).toBe(1);
         expect(result.values).toHaveLength(1);
@@ -1319,6 +1358,24 @@ describe("SearchBuilder", () => {
   });
 
   describe("isR15", () => {
+    test("R15の抽出・除外条件を両方保持する", async () => {
+      const queries: URLSearchParams[] = [];
+      server.use(
+        http.get("https://api.syosetu.com/novelapi/api/", ({ request }) => {
+          queries.push(new URL(request.url).searchParams);
+          return responseGzipOrJson([{ allcount: 0 }], new URL(request.url));
+        })
+      );
+      for (const first of [true, false]) {
+        await NarouAPI.search().gzip(0).isR15(first).isR15(!first).execute();
+      }
+      expect(queries).toHaveLength(2);
+      for (const query of queries) {
+        expect(query.get("isr15")).toBe("1");
+        expect(query.get("notr15")).toBe("1");
+      }
+    });
+
     test("default", async () => {
       const mockFn = vi.fn();
       setupMockHandler(mockFn, ["gzip", "out"]);
diff --git a/test/user-search.test.ts b/test/user-search.test.ts
index bda239b..c801a5f 100644
--- a/test/user-search.test.ts
+++ b/test/user-search.test.ts
@@ -169,11 +169,13 @@ describe("UserSearchBuilder", () => {
 
   describe("page", () => {
     describe("default count", () => {
-      test.each([1, 2, 3, 4, 5] as const)("if page = %i", async (page) => {
+      test.each([0, 1, 2, 3, 4, 5] as const)("if page = %i", async (page) => {
         const mockFn = vi.fn();
         setupMockHandler(mockFn, ["lim", "st", "gzip", "out"]);
 
         const result = await NarouAPI.searchUser().page(page).execute();
+        expect(result.start).toBe(page * 20);
+        expect(result.page).toBe(page);
         expect(result.allcount).toBe(1);
         expect(result.length).toBe(1);
         expect(result.values).toHaveLength(1);
@@ -190,11 +192,13 @@ describe("UserSearchBuilder", () => {
     });
 
     describe.each([1, 10, 100, 500] as const)("if count = %i", (count) => {
-      test.each([1, 2, 3, 4, 5] as const)("if page = %i", async (page) => {
+      test.each([0, 1, 2, 3, 4, 5] as const)("if page = %i", async (page) => {
         const mockFn = vi.fn();
         setupMockHandler(mockFn, ["lim", "st", "gzip", "out"]);
 
         const result = await NarouAPI.searchUser().page(page, count).execute();
+        expect(result.start).toBe(page * count);
+        expect(result.page).toBe(page);
         expect(result.allcount).toBe(1);
         expect(result.length).toBe(1);
         expect(result.values).toHaveLength(1);
@@ -326,6 +330,22 @@ describe("UserSearchBuilder", () => {
   });
 
   describe("name1st", () => {
+    test.each([null, "", "あ"])(
+      "ユーザーのname1st=%sを保持する",
+      async (name1st) => {
+        server.use(
+          http.get("https://api.syosetu.com/userapi/api/", ({ request }) =>
+            responseGzipOrJson([{ allcount: 1 }, { name1st }], new URL(request.url))
+          )
+        );
+        const result = await NarouAPI.searchUser()
+          .gzip(0)
+          .fields(UserFields.name1st)
+          .execute();
+        expect(result.values).toEqual([{ name1st }]);
+      }
+    );
+
     test("default", async () => {
       const mockFn = vi.fn();
       setupMockHandler(mockFn, ["gzip", "out"]);