Last week, I posted an experiment of mine: a tiny game to help me practice Hiragana and Katakana https://www.reddit.com/r/LearnJapanese/comments/1lk3qym To be honest, I didn't really have a plan for it other than share the experiment. The post was removed for not being a free resource (I understand). Having said that, it was wonderful to see lots of interest and great feedback in the comments. Really like the idea of adding N5-N1 Kanji too.
Since then, I've worked on the app some more and managed to get it on the App Store. It's listed as Mochi Invaders and it's free (no ads, tracking, etc). For now, it's configurable for either Hiragana or Katakana (or any combination of subgroups). It's early days, so you may find rough edges. Please report issues via the feedback button.
Mochi Invaders was recently approved for the App Store, so the app may not yet be found by its name on the App Store. Here's a direct link https://apps.apple.com/gb/app/mochi-invaders/id6747766176
Hope you like it.
by xenodium