If that is hard for you, then you don't have a fuckin chance with ex-rumia. >ShinyPowerMan Easy. Move your mouse away from the danmaku, wait a little, and shot her in the ass.
Found something fun. If you're able to shoot normal Rumia the song plays but mission continues.
I was surprise I got the shot myself.
*Edit I was finally able to find the source and artist...although I actually found it years ago but always felt that other would fix it before me so...sorry.
Something fiercely satisfying about wiping that smug glare on EX-Rumia clean off her face with an arm size suppository blasted up her panty-chute. (fist pump)