This is Gengetsu's theme from Touhou 4: Lotus Land Story

Nothin' innocent about you, girl.

So, she comes out to kill you after her sister is defeated. This is basically like the first ever Phantasm stage, except it's during the same stage. I GUESS YOU AREN'T SO ORIGINAL AFTER ALL, YOU GODDAMN GAPHAX-ER YOU!! (I'm naming no names, she knows who she is ¬_¬)