Loved the interpretation of the theme, and the Metroidvania mechanic was quite unique and well-executed! However, using the menu to swap between the characters all the time got a bit tiresome after a while. I think having a separate keybind that instantly switches to the next character would have been a big help (while still being able to select them manually from the main menu). On the other hand, each character having her own music theme was a cool touch and definitely contributed to the "magical girl show" feeling (although Clover definitely got the short end of the stick there).
I really liked the little bullet hell boss fights, it was cool to see everyone show up and help as you unlocked more characters! I think this is an idea that definitely has a lot of potential, especially with more different arenas and bullet patterns.