I like the funny physics that can happen with the characters (and being able to spin Reimu around)! It makes for a very unique take on the schmup concept. It also stands out to me personally due to some of the other games that I play (ex: Crypt of the Necrodancer local co-op). Also, the main portrait illustration gets a lot of good use and it's fun to look at.
I did wonder about the layout, and if there might be a way to add more visual flair to the UI elements (ex: scoreboard, leaderboard). In fact, I can see this being expanded into an entire full game, if that becomes an interest - although it does make for a good quick game as is. Well done!