Humanity's Existence Depends on Love Gambling with Another World's Princess

Lumis, the daughter of the Great Demon Lord, moves to Earth in order to pursue romance. She enrolls an all-girls school, and joins the class of the only male teacher, Kazuki. However, Kazuki quickly learns that the Great Demon Lord will destroy Earth if Lumis ever cries...!? This is the beginning of an ultimate heart-throbbing romantic comedy!