Based on the erotic manga by Kaizuka.

An alien crashes into Amano Inori and while fixing her body, makes her smarter, more athletic, prettier, and increases her bust size about five cups by accident.

The alien then requests to monitor her, since he came to Earth to monitor humans anyway, and doesn't really do anything to her until she sees Sugiuchi and Amano Inori get horny.

The alien then manipulates Amano Inori's body and makes her start having sex with Sugiuchi.