Privacy Policy

Last updated: May 2026

Kessen is a personal anime ranking tool. This page explains what data is stored when you use it, and how to have it removed.

What we store

Kessen stores the following data, and nothing else:

Your rankings and battle history — your ELO scores, wins/losses, and battle history for each anime you have ranked.
Your account identifier — your numeric AniList user ID or MyAnimeList user ID, used as a storage key to link your rankings to your account. We do not store your email address, password, or any personal information beyond this ID.
Your display name and avatar URL — fetched from AniList or MyAnimeList at login and stored locally in your browser to display your profile badge. These are not sent to our servers.

Where it's stored

In your browser — your session data (rankings, battle history) is saved to localStorage on your device. Clearing your browser data removes it.
In Netlify Blob Storage — if you are logged in via AniList or MAL OAuth, your session is also backed up to Netlify's hosted blob storage, keyed by your account ID. This enables your rankings to sync across devices. Netlify's privacy policy applies to this storage: netlify.com/privacy.
In Google Firebase Realtime Database — only when you actively use a multiplayer feature (Watch Together or Live Challenge). See the section below for what is stored and for how long.

Multiplayer (Firebase) data

Kessen's multiplayer features (Watch Together and Live Challenge) use Google's Firebase Realtime Database to coordinate state between players. This is only used when you actively start or join a multiplayer session — Firebase is not contacted for solo battling, profile viewing, or any other part of the app.

When you create or join a session, the following is written to Firebase:

Your display name as typed into the session lobby.
A randomly-generated player ID for that session.
For Watch Together: the list of anime each player nominates, the matchups generated from those nominations, and each player's votes per matchup.
For Live Challenge: the list of AniList or MyAnimeList IDs of anime you have watched (used to find matchups you've both seen), the matchups, your picks, and your predictions of your opponent's picks. This is only stored while the session is active.

Data is retained for the duration of the session and is removed when the session ends or expires. We do not store transcripts of completed games on Firebase. Firebase's privacy policy applies to this storage: firebase.google.com/support/privacy.

Authentication tokens

OAuth access tokens from AniList and MyAnimeList are stored only in your browser's localStorage. They are sent to our Netlify Functions solely to verify your identity when reading or writing your saved rankings — they are never logged, shared, or stored on our servers.

What we don't do

We do not sell or share your data with third parties.
We do not use analytics, advertising trackers, or cookies.
We do not store your watch history or scores from AniList or MyAnimeList — only the ELO rankings you build within Kessen.

Third-party services

Kessen connects to the following external services, each with their own privacy policies:

AniList — for login, fetching your anime list, and metadata.
MyAnimeList — for login and fetching your anime list.
Netlify — for hosting and cloud save storage.

Deleting your data

The easiest way to delete your data is directly from within the app. Open your rankings, go to the Manage tab, scroll to the Danger Zone, and press Delete all my data. This removes your rankings from your device and from cloud storage immediately.

If you are unable to access the app, email feedback@kessen.co.uk with your AniList or MyAnimeList username and we will remove your cloud data within 7 days. Please note that any data remaining on your device (such as in your browser or the installed app) will need to be cleared manually by clearing your browser or app data on your device.

Changes to this policy

If this policy changes in a meaningful way, a notice will be posted on the site. The date at the top of this page will always reflect the most recent update.