Install Sekai Japanese Academy

Private Android app. You need the invite code you were given. No account is needed, and your progress stays on your phone.

Download the app

Open the downloaded file. If Android asks, allow your browser to install apps (Settings → “Install unknown apps”).
Android shows its own install screen. Tap Install.
Then come back here and tap Set up updates so the app can keep itself up to date.

Set up updates in the app

The setup button only works once, on the phone where the app is installed. If it does not open the app, open the app → settings → app updates and type the same invite code.