diff --git a/packages/backend/src/mfm/to-html.ts b/packages/backend/src/mfm/to-html.ts
index 8d06b2a95..5ae4cda2a 100644
--- a/packages/backend/src/mfm/to-html.ts
+++ b/packages/backend/src/mfm/to-html.ts
@@ -113,21 +113,21 @@ export async function toHtml(
 			return a;
 		},
 
-		mention(node) {
+		async mention(node) {
 			const { username, host, acct } = node.props;
-			const href = resolveMentionFromCache(username, host, objectHost, mentionedRemoteUsers);
+			const resolved = await resolveMentionFromCache(username, host, objectHost, mentionedRemoteUsers);
 
 			const el = doc.createElement("span");
-			if (href === null) {
+			if (resolved === null) {
 				el.textContent = acct;
 			} else {
 				el.setAttribute("class", "h-card");
 				el.setAttribute("translate", "no");
 				const a = doc.createElement("a");
-				a.href = href;
+				a.href = resolved.href;
 				a.className = "u-url mention";
 				const span = doc.createElement("span");
-				span.textContent = username;
+				span.textContent = resolved.username;
 				a.textContent = '@';
 				a.appendChild(span);
 				el.appendChild(a);
diff --git a/packages/backend/src/remote/resolve-user.ts b/packages/backend/src/remote/resolve-user.ts
index 13cddc2d8..b2fa71432 100644
--- a/packages/backend/src/remote/resolve-user.ts
+++ b/packages/backend/src/remote/resolve-user.ts
@@ -13,6 +13,7 @@ import { IMentionedRemoteUsers } from "@/models/entities/note.js";
 
 const logger = remoteLogger.createSubLogger("resolve-user");
 const uriHostCache = new Cache<string>("resolveUserUriHost", 60 * 60 * 24);
+const localUsernameCache = new Cache<string | null>("localUserNameCapitalization", 60 * 60 * 24);
 
 export async function resolveUser(
 	username: string,
@@ -184,7 +185,6 @@ export async function resolveUser(
 
 export async function resolveMentionToUserAndProfile(username: string, host: string | null, objectHost: string | null) {
 	try {
-		//const fallback = getMentionFallbackUri(username, host, objectHost);
 		const user = await resolveUser(username, host ?? objectHost, false);
 		const profile = await UserProfiles.findOneBy({ userId: user.id });
 		const data = { username, host: host ?? objectHost };
@@ -206,12 +206,30 @@ export function getMentionFallbackUri(username: string, host: string | null, obj
 	return fallback;
 }
 
-export function resolveMentionFromCache(username: string, host: string | null, objectHost: string | null, cache: IMentionedRemoteUsers): string | null {
-	const fallback = getMentionFallbackUri(username, host, objectHost);
+async function getLocalUsernameCached(username: string): Promise<string | null> {
+	return localUsernameCache.fetch(username.toLowerCase(), () =>
+		Users.findOneBy({ usernameLower: username.toLowerCase(), host: IsNull() })
+			.then(p => p ? p.username : null));
+}
 
+export async function resolveMentionFromCache(username: string, host: string | null, objectHost: string | null, cache: IMentionedRemoteUsers): Promise<{ username: string, href: string } | null> {
+	const isLocal = (host === null && objectHost === null) || host === config.domain;
+	if (isLocal) {
+		const finalUsername = await getLocalUsernameCached(username);
+		if (finalUsername === null) return null;
+		username = finalUsername;
+	}
+	try {
+		if (isLocal) username = await resolveUser(username, null).then(p => p?.username ?? username);
+	} catch {
+		return null;
+	}
+
+	const fallback = getMentionFallbackUri(username, host, objectHost);
 	const cached = cache.find(r => r.username.toLowerCase() === username.toLowerCase() && r.host === host);
-	if (cached) return cached.url ?? cached.uri ?? fallback;
-	if ((host === null && objectHost === null) || host === config.domain) return fallback;
+	const href = cached?.url ?? cached?.uri;
+	if (cached && href != null) return { username: cached.username, href: href };
+	if (isLocal) return { username: username, href: fallback };
 	return null;
 }
 
diff --git a/packages/backend/src/server/api/mastodon/helpers/mfm.ts b/packages/backend/src/server/api/mastodon/helpers/mfm.ts
index 055ac9110..c1f69e3af 100644
--- a/packages/backend/src/server/api/mastodon/helpers/mfm.ts
+++ b/packages/backend/src/server/api/mastodon/helpers/mfm.ts
@@ -135,21 +135,21 @@ export class MfmHelpers {
                 return a;
             },
 
-            mention(node) {
+            async mention(node) {
                 const { username, host, acct } = node.props;
-                const href = resolveMentionFromCache(username, host, objectHost, mentionedRemoteUsers);
+                const resolved = await resolveMentionFromCache(username, host, objectHost, mentionedRemoteUsers);
 
                 const el = doc.createElement("span");
-                if (href === null) {
+                if (resolved === null) {
                     el.textContent = acct;
                 } else {
                     el.setAttribute("class", "h-card");
                     el.setAttribute("translate", "no");
                     const a = doc.createElement("a");
-                    a.href = href;
+                    a.href = resolved.href;
                     a.className = "u-url mention";
                     const span = doc.createElement("span");
-                    span.textContent = username;
+                    span.textContent = resolved.username;
                     a.textContent = '@';
                     a.appendChild(span);
                     el.appendChild(a);