Yukitaka has just left Tokyo, eager to transfer to Kisaragi High where he's been recruited to play baseball. However, upon entering his new apartment, the boy is met by a man with long blonde hair who claims to be… an alien?! After initially scoffing at the notion, Yukitaka discovers that the alien – Ouji – is for real, has amnesia and, what's worse, now wants to live with him in his apartment. The fact that scientists and mysterious guys in black suits are after Ouji becomes the least of Yukitaka's problems as his new guest turns out to be more than a handful to handle!