Mizuchi, unhinged vengeful spirit from old hell dislikes the lack of chaos in the current Gensokyo - and doesn't mind helping the "unnatural order" collapse.
Furthermore, it seems she doesn’t want her actions to go unnoticed
She can possess people, taking complete control of their body and their abilities. Her victims have no memories of anything that happened during the time that they were possessed. If Used On Youkai, They will fall into a coma by draining all of their magical Energy, Touhou