I totally understand, I hate having to mash the shot button in shmups too, but that's why I made it so pressing the button once makes cirno shoot for long enough that you can actually just wait a second or two between each button press without sacrificing firing speed, and just tap at a slow rhythmic pace if it's tiring for you.
Also in retrospect I really wish I went through with giving mokou a halfway checkpoint. I toned down her danmaku a lot, but I really wanted to make a game anyone could beat!