From MangaHelpers:
Hoshino Shiho is known in school as a major delinquent, and there are even three students who repeatedly ask her to be a part of her 'gang.' While Shiho does talk pretty rough, and she does beat up bullies when they're in her way, she really doesn't think of herself as a delinquent.
One night, in her family's hot spring inn, a spaceship crashes into the bathhouse. The alien from inside, "Dejiraoki Seco Omega," claims he has come to conquer and destroy Earth, as he has destroyed many planets before it. Luckily for Shiho, another alien soon shows up and manages to leash Omega to a video-game-like controller.
Finding herself in possession of this controller, Shiho promptly uses it to force him to take responsibility for the mess he's made of the bathhouse. Now Shiho has an angry alien under her control, but who knows what else is out there to threaten the Earth?