Sundome!! Milky Way Vol. 3 (manga)

NUT UP OR SHUT UP

Yoshitake, the world's horniest man, has ditched Lune-the universe's sexiest alien who came to Earth for his sperm-to date his innocent co-worker Yuizono Haruka. Another co-worker, Mika, is hot (and hotheaded) with sexual secrets of her own, finds herself trapped in a gym locker with Yoshitake where it's getting more cramped by the moment. But if he ever ejaculates into an Earth woman, Lune's entire species is doomed to extinction! It's a hard time to be hard up!