It's a BM simulator that auto-plays the notes, but when a note is played, bullets fly across the screen. The little player-character has to dodge all the bullets until the end of the song.
There's a 'shield bonus' as well... if a certain amount of bullets hit the shield (but not the player!), a short invincibility occurs (the player can clear the screen of bullets this way)
It's fun and crazy
MixWaver 1's Bonus mode is similar in a way. The notes fall down and fire bullets randomly, but the player can fire back and destroy the notes. No auto-fire in it though, so it's hard.
Also, LR wasn't that difficult to install. Took me 6 minutes with the sticky, though I'd already had the Japanese Language pack installed cause I'm a weeaboo fag.