Giving this a shot thank you for sharing! A bit of a tangent here...It might just be me, but I always struggle with confusing similar characters together (I don't handwrite so happens often especially when I see them out of context). I find when using ANKI that I think I know a character but I only know it relative to the set of characters I'm learning. That character is considered learned, but when a new character that's similar gets added, I have to essentially relearn both. I built a very simple tool integrating Anki with ios shortcuts to get me to quickly add commonly confused characters and then test me on those characters specifically. I found that helped me a lot but isn't an ideal solution. If this is a common issue with others, it might be something to consider adding!

Some initial thoughts + feedback on the app: Overwhelming! It might be worth creating a very very simple guided process to get people clicking and playing right away, and then the ability to dig deeper and customize your cards can be done later. Adding from a list of too many options feels a bit dizzying. There could be an auto-mode that lets me get a feel of the app first then later can go 'oh I can customize'