Average Guy meets the perfect girlfriend from another world. ("Magical Girlfriends" anime)
Anime
A very basic, yet common trope in anime. A normal guy, typically down on his luck finally meets the perfect girl! She just shows up in his life. But she's not from earth. She's an alien or is some kind of other otherworldly being.

TV, 2015,
12 eps
Me:-
Author:10
Various subspecies, most common Half Animal/Half Human

OVA, 2005,
4 eps
Me:-
Author:6
Angel (More of a parody of the genre as Dokuro isn't really "Perfect")

OVA, 1992,
6 eps
Me:-
Author:8
I believe she's technically human but she's not from our world as she comes out from a video tape.