We use Firebase Auth and store your email/UID for sign-in. We keep a user profile with username, avatar, role, points, plan/usage data. Game state/history stored per user. We may store problem reports and optional message screen labels. AI question generation uses OpenAI API; requests include selected categories/difficulty and avoid blocked facts. Generated question content is stored in questions db and per-user session state. Friend/social features store relationships and leaderboard profile snapshots. We enforce rate limits and admin checks. No explicit third-party analytics shown; data is only in Firestore + Cloud Functions.