Sora Hoshino is an unassuming college student who loves astronomy. One day, a handsome man appears before Sora completely nude, and introduces himself as Regulus, prince of a dying alien species with an extremely low fertility rate. While scouting for a new breeding partner, Regulus has been watching Sora from space, and asks for his hand in marriage. Sora has his doubts, but Regulus's tentacles and mysterious cosmic powers feel too good to resist...