diff --git a/src/idz/db/backgrounds.ts b/src/idz/db/backgrounds.ts
new file mode 100644
index 0000000..9f055d0
--- /dev/null
+++ b/src/idz/db/backgrounds.ts
@@ -0,0 +1,55 @@
+import { Client } from "pg";
+import * as sql from "sql-bricks";
+
+import { _findProfile } from "./_util";
+import { BackgroundCode, ExtId } from "../model/base";
+import { Profile } from "../model/profile";
+import { FlagRepository } from "../repo";
+import { generateId } from "../../db";
+
+export class SqlBackgroundsRepository
+  implements FlagRepository<BackgroundCode> {
+  constructor(private readonly _conn: Client) {}
+
+  async loadAll(extId: ExtId<Profile>): Promise<Set<BackgroundCode>> {
+    const loadSql = sql
+      .select("bg.background_no")
+      .from("idz.background_unlock bg")
+      .join("idz.profile p", { "bg.profile_id": "p.id" })
+      .where("p.ext_id", extId)
+      .toParams();
+
+    const { rows } = await this._conn.query(loadSql);
+    const result = new Set<BackgroundCode>();
+
+    for (const row of rows) {
+      result.add(row.background_no);
+    }
+
+    return result;
+  }
+
+  async saveAll(
+    extId: ExtId<Profile>,
+    flags: Set<BackgroundCode>
+  ): Promise<void> {
+    const profileId = await _findProfile(this._conn, extId);
+    const existing = await this.loadAll(extId);
+
+    for (const flag of flags) {
+      if (existing.has(flag)) {
+        continue;
+      }
+
+      const saveSql = sql
+        .insert("idz.background_unlock", {
+          id: generateId(),
+          profile_id: profileId,
+          background_no: flag,
+        })
+        .toParams();
+
+      await this._conn.query(saveSql);
+    }
+  }
+}