The following post contains some comically adult subject matter.
Harley Quinn (Batman) and Squall (Final Fantasy VIII)... "What do you mean you don't want to dance with me, Squall? You danced with that happy-go-lucky chick in blue!" "..." "Don't just move your head like that, say something!"
Fleur Delacour (Harry Potter) and Ash (Evil Dead)... "All right, Fleur...THIS...is my BOOMSTICK!" "Eet's so beeg!"
Duke Nukem (Duke Nukem game series) and Dante (Devil May Cry game series)... "I'm going to kick ass and chew demon cum...but I'm all out of cum." "I'll help you with that, Dukie. Ung...JACKPOT!"
Death (The Sandman comics) and the Johnny the Homocidal Maniac (from the JTHM comics). C'mon, they're perfect for each other--if Nny went nuts and tried to kill her like for any of his other girlfriends, he would fail and she wouldn't die, because she's Death! Plus, she has to like him because he brings so many people to her clutches. The only problem, I think, would be that Death likes Marry Poppins, which Nny would never tollerate.
Harley Quinn (Batman) and The Doughboys (from the JTHM comics). "The last guy I tried dating was dull and standoffish. Will you two be better?" "Only if you kill yourself!" "No, don't listen to him. Kill other people! Kill them all!" "No, kill yourself! You're a failure as a human being, Harley!" *Harley cries* "f**k all you guys, I'm going back to Mr. J!" *Doughboys stare at each other* "Well look what you did now! Why don't you go kill yourself, you miserable excuse for a Pillsbury?"
Cthulhu and Hentai Schoolgirl Chick #12. "OH GOD! NO! NO! DON'T TENTACLE RAPE ME! OH NO! NO! YES! NO! YES, YES, NO! YES! IT FEELS SO GOOD! AAAAAH! AAAAGH I'M GOING TO CUM!"
Luna Lovegood (Harry Potter) and Delierium (The Sandman), the two weirdest, airy-est girls in fantasy fiction. I don't think they'd become lesbian lovers or anything, but they could be best friends.
Severus Snape (Harry Potter) and Selene (Underworld). Ah, what a decadent gothic romance that would be.
Edward Scissorhands and Pyramid Head (from Silent Hill). THAT would be friggin' WEIRD.