Really fun gameplay, graphics is very minimalistic but it gets the job done, I had to try hard a bit but I haven't died once!
I don't know if it's a thing already, I think it's not, but consider adding an immunity frame during the dash, I think it would the game more fun but maybe a little bit easier! Also I don't know if it's intended but I found that standing in the corners of the map as far away as possible from the boss might be the best strategy since you can keep charging your flow bar easily.
Very good game overall, challenging and fun! Good job!