Just an update on this. I couldn’t find this app in the app store on my iPad so I contacted the Publisher. The app is being updated and it offline for a period of time. It is unknown when the app will be back, but it will be back.
For Japanese learning games, I would like to recommend:
Learn Japanese to survive - Hiragana battle and
Learn Japanese to survive - Katakana battle. Both available on Steam. Kanji battle is also coming, but still being developed.