I was pretty happy with my 50 chain by the time I got to the boss, but looking at Mantou's score, it probably wasn't that impressive.
Also, for some reason, my combo was significantly lower than my chain. Bug?
Anyway, interesting and fun game! The control scheme definitely has a learning curve, but it was fun to figure it out. The art and music were both top-notch, too.
Gameplay wise, with the way enemy bullets block your bullets, it can get out of control pretty quickly, especially if you drop below 4 power, but that could well be a feature. It makes it a bit volatile in terms of RNG, though.
Also, a slightly more responsive version of the same control scheme might be "hold space to go up, release space to go down", or something like that. I'm not sure if this would actually feel good, but perhaps? I think I tended to hold the button after pressing it anyway, so changing states both required a release and a re-press for me.