Akane Acrave Stain

A space alien who crash lands on Earth, claiming to be Hiroki's fiancee and kisses him, and on the next day, transfers to his class. According to this girl, a kiss equals marriage. Despite Hiroki refusing to accept his fate, Akane never gives up because of her love! Aside from being very affectionate with Hiroki, Akane is also very honest about herself and her feelings.

She claims that she is a cousin to Urusei Yatsura's Lum.

Spoiler

Though the two are unaware of the relationship, she is Hiroki's sister.