Squad system.

[Kryvytsky]

Limit number of anime girls by 3. This would let to create more than 9 playable characters and remove confusing at numbers, cuz it's annoying when for example Sei changes keyboard number by progress of game.

Also, how can I export game data on other device?

[Anuken]

Frankly I don't think characters should be switchable in a level at all; it's a weird mechanic to have in a rhythm game and interrupts the movement. In the future, you should have one character selected at the start of the level, or maybe even two characters being controlled at once (WASD and arrow keys).

[Kryvytsky]

If only one character available, what about level 3 and 4? As I remember there is parts with waves of conveyors that is not possible to dodge by solo Mono and Oct.
Control two characters at once sound too difficult. Even with one would be hard to beat some levels. But I think that's interesting idea for coop playing with friends. As I remember a lot of games in past have coop mode like one control by WASD and other one by arrow keys.

[Anuken]

As I remember there is parts with waves of conveyors that is not possible to dodge by solo Mono and Oct.

I would either need to add some sort of damage ability to those, or make a damage-dealing character follow behind or something. I just don't like the idea of "magically" switching between characters, feels weird and clunky

Control two characters at once sound too difficult.

That's kind of the idea, it's a lot harder. It probably wouldn't work for most levels.

[Kryvytsky]

I just don't like the idea of "magically" switching between characters, feels weird and clunky

I get it. Currently it looks like in Genshin impact. What about add some animation for switching? Like in fighting game? I once played Skull Girls you can change characters and they play a specific animation when they enter the fight.