diff --git a/app/web/src/components/pages/WatchBody.tsx b/app/web/src/components/pages/WatchBody.tsx
index 6003403..ffb691e 100644
--- a/app/web/src/components/pages/WatchBody.tsx
+++ b/app/web/src/components/pages/WatchBody.tsx
@@ -628,6 +628,11 @@ function WatchInner(props: { locale: Locale; mediaItemId: string }) {
             <div className="flex flex-wrap items-center justify-between gap-2 text-sm text-muted-foreground">
                 <span className="flex flex-wrap items-center gap-2">
                     <span>{sourceLabel}</span>
+                    {isLocalSource && fetchMessage.includes("同名") && (
+                        <span className="rounded bg-primary/10 px-1.5 py-0.5 text-[11px] text-primary">
+                            {t(locale, "watch.sidecarLinked")}
+                        </span>
+                    )}
                     {showRematch && (
                         <Button size="sm" variant="outline" onClick={openRematch}>
                             {t(locale, "watch.rematch")}
diff --git a/packages/i18n/src/messages/en.ts b/packages/i18n/src/messages/en.ts
index 8ce6677..75d6880 100644
--- a/packages/i18n/src/messages/en.ts
+++ b/packages/i18n/src/messages/en.ts
@@ -182,6 +182,7 @@ export const en: Record<MessageKey, string> = {
     "watch.matchManual": "Manual match",
     "watch.importSaved": "Danmaku saved",
     "watch.foundSameName": "Same-name candidate",
+    "watch.sidecarLinked": "Same-name danmaku",
     "watch.filterTitle": "Danmaku filters",
     "watch.blockKeywordAdd": "Add block word",
     "watch.matchFailed": "Danmaku match failed",
diff --git a/packages/i18n/src/messages/zh-CN.ts b/packages/i18n/src/messages/zh-CN.ts
index b2a7a00..9aebcab 100644
--- a/packages/i18n/src/messages/zh-CN.ts
+++ b/packages/i18n/src/messages/zh-CN.ts
@@ -177,6 +177,7 @@ export const zhCN = {
     "watch.matchManual": "手动匹配",
     "watch.importSaved": "弹幕已保存",
     "watch.foundSameName": "同名候选",
+    "watch.sidecarLinked": "同名弹幕",
     "watch.filterTitle": "弹幕过滤",
     "watch.blockKeywordAdd": "添加屏蔽词",
     "watch.matchFailed": "弹幕匹配失败",
diff --git a/packages/trpc/src/services/danmaku.service.test.ts b/packages/trpc/src/services/danmaku.service.test.ts
index 6292169..441b0f7 100644
--- a/packages/trpc/src/services/danmaku.service.test.ts
+++ b/packages/trpc/src/services/danmaku.service.test.ts
@@ -1,13 +1,15 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
 import { openCommentXml, openCommentsToXml, openMatch, hasOpenCredentials } from "@app/danmaku";
-import { danmakuCacheDao, danmakuDocsDao, danmakuPrefsDao, mediaItemDao } from "@app/dao";
+import { danmakuCacheDao, danmakuDocsDao, danmakuPrefsDao, mediaItemDao, mountDao } from "@app/dao";
 import type {
     DanmakuCacheRow,
     DanmakuDocRow,
     DanmakuPrefsRow,
     MediaItem as MediaItemRow,
+    Mount,
 } from "@app/models";
 import { danmakuService } from "./danmaku.service.js";
+import { createWebdav } from "./webdav-client.js";
 
 vi.mock("@app/dao", () => ({
     danmakuCacheDao: { getValid: vi.fn(), upsert: vi.fn() },
@@ -20,6 +22,14 @@ vi.mock("@app/dao", () => ({
     mountDao: { getByIdForUser: vi.fn() },
 }));
 
+vi.mock("./webdav-client.js", async (importOriginal) => {
+    const actual = await importOriginal<typeof import("./webdav-client.js")>();
+    return {
+        ...actual,
+        createWebdav: vi.fn(),
+    };
+});
+
 vi.mock("@app/danmaku", async (importOriginal) => {
     const actual = await importOriginal<typeof import("@app/danmaku")>();
     return {
@@ -94,6 +104,49 @@ function prefsRow(over: Partial<DanmakuPrefsRow> = {}): DanmakuPrefsRow {
     };
 }
 
+function mountRow(over: Partial<Mount> = {}): Mount {
+    return {
+        id: "mnt1",
+        userId: "u1",
+        name: "nas",
+        type: "webdav",
+        baseUrl: "https://dav.example.com",
+        username: null,
+        secretEnc: "",
+        rootPath: "/library",
+        enabled: true,
+        createdAt: new Date(),
+        updatedAt: new Date(),
+        ...over,
+    };
+}
+
+type FakeEntry = {
+    filename: string;
+    basename: string;
+    type: "file" | "directory";
+    size: number;
+};
+
+function fakeWebdavClient(opts: {
+    entries?: FakeEntry[];
+    contents?: string;
+    listError?: Error;
+    readError?: Error;
+}) {
+    return {
+        getDirectoryContents: vi.fn().mockImplementation(async () => {
+            if (opts.listError) throw opts.listError;
+            return opts.entries ?? [];
+        }),
+        getFileContents: vi.fn().mockImplementation(async () => {
+            if (opts.readError) throw opts.readError;
+            return Buffer.from(opts.contents ?? "", "utf8");
+        }),
+        createReadStream: vi.fn(),
+    };
+}
+
 beforeEach(() => {
     vi.clearAllMocks();
 });
@@ -364,3 +417,213 @@ describe("openCommentsToXml（@app/danmaku，p 序列化 8 段）", () => {
         ).toBe('<?xml version="1.0" encoding="UTF-8"?><i></i>');
     });
 });
+
+describe("danmakuService.ensureSidecarXml", () => {
+    const sidecarXml = '<i><d p="1,1,0,0,0,0,,">hi</d></i>';
+
+    function setupMounted(over: Partial<MediaItemRow> = {}) {
+        vi.mocked(mediaItemDao.getByIdForUser).mockResolvedValue(
+            mediaItem({ mountId: "mnt1", ...over }),
+        );
+        vi.mocked(mountDao.getByIdForUser).mockResolvedValue(mountRow());
+    }
+
+    it("同目录同名 .xml 侧车：读全文落 local-xml，返回 true", async () => {
+        setupMounted({ path: "/anime/[Sub] Title - 01.mkv" });
+        vi.mocked(createWebdav).mockReturnValue(
+            fakeWebdavClient({
+                entries: [
+                    {
+                        filename: "/library/anime/[Sub] Title - 01.xml",
+                        basename: "[Sub] Title - 01.xml",
+                        type: "file",
+                        size: sidecarXml.length,
+                    },
+                ],
+                contents: sidecarXml,
+            }) as never,
+        );
+        const ok = await danmakuService.ensureSidecarXml("u1", "m1");
+        expect(ok).toBe(true);
+        expect(danmakuDocsDao.upsert).toHaveBeenCalledWith({
+            userId: "u1",
+            mediaItemId: "m1",
+            source: "local-xml",
+            xml: sidecarXml,
+            byteSize: Buffer.byteLength(sidecarXml, "utf8"),
+        });
+    });
+
+    it("扩展名 .XML 大小写不敏感同样命中", async () => {
+        setupMounted({ path: "/anime/Show - 02.mkv" });
+        vi.mocked(createWebdav).mockReturnValue(
+            fakeWebdavClient({
+                entries: [
+                    {
+                        filename: "/library/anime/SHOW - 02.XML",
+                        basename: "SHOW - 02.XML",
+                        type: "file",
+                        size: sidecarXml.length,
+                    },
+                ],
+                contents: sidecarXml,
+            }) as never,
+        );
+        await expect(danmakuService.ensureSidecarXml("u1", "m1")).resolves.toBe(true);
+    });
+
+    it("仅同 basename 的 .xml 命中：别的名/别的扩展/目录均跳过", async () => {
+        setupMounted({ path: "/anime/Show - 02.mkv" });
+        const client = fakeWebdavClient({
+            entries: [
+                {
+                    filename: "/library/anime/Show - 03.xml",
+                    basename: "Show - 03.xml",
+                    type: "file",
+                    size: 10,
+                },
+                {
+                    filename: "/library/anime/Show - 02.srt",
+                    basename: "Show - 02.srt",
+                    type: "file",
+                    size: 10,
+                },
+                {
+                    filename: "/library/anime/Show - 02.xml",
+                    basename: "Show - 02.xml",
+                    type: "directory",
+                    size: 0,
+                },
+            ],
+            contents: sidecarXml,
+        });
+        vi.mocked(createWebdav).mockReturnValue(client as never);
+        await expect(danmakuService.ensureSidecarXml("u1", "m1")).resolves.toBe(false);
+        expect(danmakuDocsDao.upsert).not.toHaveBeenCalled();
+        expect(client.getFileContents).not.toHaveBeenCalled();
+    });
+
+    it("侧车超过 20MB：不读文件直接跳过", async () => {
+        setupMounted({ path: "/anime/Show - 02.mkv" });
+        const client = fakeWebdavClient({
+            entries: [
+                {
+                    filename: "/library/anime/Show - 02.xml",
+                    basename: "Show - 02.xml",
+                    type: "file",
+                    size: 20_000_001,
+                },
+            ],
+            contents: sidecarXml,
+        });
+        vi.mocked(createWebdav).mockReturnValue(client as never);
+        await expect(danmakuService.ensureSidecarXml("u1", "m1")).resolves.toBe(false);
+        expect(client.getFileContents).not.toHaveBeenCalled();
+        expect(danmakuDocsDao.upsert).not.toHaveBeenCalled();
+    });
+
+    it("非弹幕粗检（无 <d ）跳过", async () => {
+        setupMounted({ path: "/anime/Show - 02.mkv" });
+        vi.mocked(createWebdav).mockReturnValue(
+            fakeWebdavClient({
+                entries: [
+                    {
+                        filename: "/library/anime/Show - 02.xml",
+                        basename: "Show - 02.xml",
+                        type: "file",
+                        size: 20,
+                    },
+                ],
+                contents: "<html>not danmaku</html>",
+            }) as never,
+        );
+        await expect(danmakuService.ensureSidecarXml("u1", "m1")).resolves.toBe(false);
+        expect(danmakuDocsDao.upsert).not.toHaveBeenCalled();
+    });
+
+    it("列目录/读取失败静默跳过不抛", async () => {
+        setupMounted({ path: "/anime/Show - 02.mkv" });
+        vi.mocked(createWebdav).mockReturnValue(
+            fakeWebdavClient({ listError: new Error("dav down") }) as never,
+        );
+        await expect(danmakuService.ensureSidecarXml("u1", "m1")).resolves.toBe(false);
+
+        vi.mocked(createWebdav).mockReturnValue(
+            fakeWebdavClient({
+                entries: [
+                    {
+                        filename: "/library/anime/Show - 02.xml",
+                        basename: "Show - 02.xml",
+                        type: "file",
+                        size: 20,
+                    },
+                ],
+                readError: new Error("boom"),
+            }) as never,
+        );
+        await expect(danmakuService.ensureSidecarXml("u1", "m1")).resolves.toBe(false);
+        expect(danmakuDocsDao.upsert).not.toHaveBeenCalled();
+    });
+
+    it("媒体无挂载/挂载失效：返回 false 且不建客户端", async () => {
+        vi.mocked(mediaItemDao.getByIdForUser).mockResolvedValue(mediaItem({ mountId: null }));
+        await expect(danmakuService.ensureSidecarXml("u1", "m1")).resolves.toBe(false);
+
+        vi.mocked(mediaItemDao.getByIdForUser).mockResolvedValue(mediaItem({ mountId: "mnt1" }));
+        vi.mocked(mountDao.getByIdForUser).mockResolvedValue(null);
+        await expect(danmakuService.ensureSidecarXml("u1", "m1")).resolves.toBe(false);
+        expect(createWebdav).not.toHaveBeenCalled();
+    });
+});
+
+describe("danmakuService.fetch 同名侧车", () => {
+    const sidecarXml = '<i><d p="1,1,0,0,0,0,,">side</d></i>';
+
+    it("无 local-xml 时自动关联侧车：返回 local-xml 且 message 含同名提示", async () => {
+        vi.mocked(mediaItemDao.getByIdForUser).mockResolvedValue(
+            mediaItem({ mountId: "mnt1", path: "/anime/Show - 01.mkv" }),
+        );
+        vi.mocked(mountDao.getByIdForUser).mockResolvedValue(mountRow());
+        vi.mocked(createWebdav).mockReturnValue(
+            fakeWebdavClient({
+                entries: [
+                    {
+                        filename: "/library/anime/Show - 01.xml",
+                        basename: "Show - 01.xml",
+                        type: "file",
+                        size: sidecarXml.length,
+                    },
+                ],
+                contents: sidecarXml,
+            }) as never,
+        );
+        vi.mocked(danmakuDocsDao.get)
+            .mockResolvedValueOnce(null)
+            .mockResolvedValueOnce(docRow({ xml: sidecarXml }));
+        const r = await danmakuService.fetch("u1", "m1");
+        expect(r.ok).toBe(true);
+        expect(r.source).toBe("local-xml");
+        expect(r.xml).toBe(sidecarXml);
+        expect(r.message).toContain("同名");
+        expect(openMatch).not.toHaveBeenCalled();
+    });
+
+    it("侧车未命中时继续走开放网络前置（缺配置时明示）", async () => {
+        vi.mocked(mediaItemDao.getByIdForUser).mockResolvedValue(mediaItem({ mountId: "mnt1" }));
+        vi.mocked(mountDao.getByIdForUser).mockResolvedValue(mountRow());
+        vi.mocked(createWebdav).mockReturnValue(fakeWebdavClient({ entries: [] }) as never);
+        vi.mocked(danmakuDocsDao.get).mockResolvedValue(null);
+        vi.mocked(hasOpenCredentials).mockReturnValue(false);
+        const r = await danmakuService.fetch("u1", "m1");
+        expect(r.source).toBe("none");
+        expect(r.message).toContain("OPEN_DANMAKU_APP_ID");
+    });
+
+    it("已有 local-xml 时不扫描侧车", async () => {
+        vi.mocked(mediaItemDao.getByIdForUser).mockResolvedValue(mediaItem());
+        vi.mocked(danmakuDocsDao.get).mockResolvedValue(docRow({ xml: "<i>local</i>" }));
+        const r = await danmakuService.fetch("u1", "m1");
+        expect(r).toEqual({ ok: true, source: "local-xml", xml: "<i>local</i>" });
+        expect(createWebdav).not.toHaveBeenCalled();
+    });
+});
diff --git a/packages/trpc/src/services/danmaku.service.ts b/packages/trpc/src/services/danmaku.service.ts
index d621a3a..8a65c7c 100644
--- a/packages/trpc/src/services/danmaku.service.ts
+++ b/packages/trpc/src/services/danmaku.service.ts
@@ -12,9 +12,26 @@ import {
 } from "@app/danmaku";
 import type { DanmakuFetchOutput, DanmakuMatchOutput, DanmakuSettingsOutput } from "@app/types";
 import { decryptSecret } from "./secret.js";
-import { createWebdav, joinWebdavPath } from "./webdav-client.js";
+import { createWebdav, joinWebdavPath, listDirectory, type DirEntry } from "./webdav-client.js";
 
 const CACHE_TTL_MS = 24 * 60 * 60 * 1000;
+/** 同名侧车 XML 全文上限，与 importXml 一致 */
+const SIDECAR_MAX_BYTES = 20_000_000;
+
+/** 媒体路径 → 所在目录（"" 表示挂载根）+ 去扩展名 basename */
+function splitDirBase(path: string): { dir: string; base: string } {
+    const norm = path.replace(/\\/g, "/");
+    const idx = norm.lastIndexOf("/");
+    const dir = idx >= 0 ? norm.slice(0, idx) : "";
+    const file = idx >= 0 ? norm.slice(idx + 1) : norm;
+    const dot = file.lastIndexOf(".");
+    return { dir, base: dot > 0 ? file.slice(0, dot) : file };
+}
+
+/** 同 basename + .xml，扩展名与 stem 均大小写不敏感 */
+function isSidecarName(fileName: string, base: string): boolean {
+    return fileName.toLowerCase() === `${base}.xml`.toLowerCase();
+}
 
 function matchKeyFor(path: string, size: number): string {
     return createHash("sha256").update(`${path}:${size}`).digest("hex");
@@ -70,6 +87,46 @@ async function persistOpenCache(episodeId: number, xml: string): Promise<void> {
 }
 
 export const danmakuService = {
+    /** 同目录同名 .xml 侧车 → 落 local-xml；失败/超限/非弹幕一律静默 false */
+    async ensureSidecarXml(userId: string, mediaItemId: string): Promise<boolean> {
+        try {
+            const item = await mediaItemDao.getByIdForUser(mediaItemId, userId);
+            if (!item?.mountId) return false;
+            const mount = await mountDao.getByIdForUser(item.mountId, userId);
+            if (!mount) return false;
+            const { dir, base } = splitDirBase(item.path);
+            if (!base) return false;
+            const client = createWebdav({
+                baseUrl: mount.baseUrl,
+                username: mount.username ?? undefined,
+                password: mount.secretEnc ? decryptSecret(mount.secretEnc) : undefined,
+            });
+            const listAbs = joinWebdavPath(mount.rootPath || "/", dir || "/");
+            const entries = await listDirectory(client, listAbs);
+            const hit = entries.find(
+                (e: DirEntry) => e.type === "file" && isSidecarName(e.basename, base),
+            );
+            if (!hit || hit.size > SIDECAR_MAX_BYTES) return false;
+            const raw = (await client.getFileContents(hit.filename, {
+                format: "binary",
+            })) as Uint8Array;
+            const buf = Buffer.isBuffer(raw) ? raw : Buffer.from(raw);
+            if (buf.byteLength > SIDECAR_MAX_BYTES) return false;
+            const xml = buf.toString("utf8");
+            if (!xml.includes("<d ")) return false;
+            await danmakuDocsDao.upsert({
+                userId,
+                mediaItemId,
+                source: "local-xml",
+                xml,
+                byteSize: Buffer.byteLength(xml, "utf8"),
+            });
+            return true;
+        } catch {
+            return false;
+        }
+    },
+
     async fetch(userId: string, mediaItemId: string): Promise<DanmakuFetchOutput> {
         const item = await mediaItemDao.getByIdForUser(mediaItemId, userId);
         if (!item) return { ok: false, source: "none", xml: "", message: "媒体不存在" };
@@ -77,6 +134,17 @@ export const danmakuService = {
         const local = await danmakuDocsDao.get(userId, mediaItemId, "local-xml");
         if (local) return { ok: true, source: "local-xml", xml: local.xml };
 
+        // 同目录同名 .xml 侧车自动关联；命中即按 local-xml 返回
+        if (await danmakuService.ensureSidecarXml(userId, mediaItemId)) {
+            const linked = await danmakuDocsDao.get(userId, mediaItemId, "local-xml");
+            return {
+                ok: true,
+                source: "local-xml",
+                xml: linked?.xml ?? "",
+                message: "同名弹幕",
+            };
+        }
+
         if (!hasOpenCredentials()) {
             return {
                 ok: true,