Who is it, and which Champion(s) does this hero/heroine bond with?
My pick would be Aqua from Kingdom Hearts: BBS, and she would get along best with Leona and Lux.
(ITT: Don't ask how that "transported to Runeterra" thing happens.)
If Ryu from Street fighter crossed over, he would train with 
a lot
Who is it, and which Champion(s) does this hero/heroine bond with?
My pick would be Aqua from Kingdom Hearts: BBS, and she would get along best with Leona and Lux.
(ITT: Don't ask how that "transported to Runeterra" thing happens.)
Not to self...get off my lazy ass and write this fanfiction like I said I would...
The only game series ive played that I can compare to League with any accuracy is Blazblue. So given this ill select my main Makoto Nanaya.
Would likely bond with Ahri the most, given that shes been treated like a second class citizen most of her life due to discrimination that "beast kin" suffer in the story. Theyre made fun of as animals and monsters, mostly due to jealousy or fear (theyre naturally pretty badass.) This would appeal well to Ahri's ever burning question "What is human?", being that the eyes, ears, nose and mouth don't define humanity at all. And Makoto isnt the type to judge Ahri killing the shit out of a bunch of stupid guys.
Balthier from Final Fantasy XII would contend the spotlight with Draven xD
And would bond with Ahri 
and Battle Bunny Riven 
because he needs a sidechick a bit animal-like. probably Riven will smash his face with the sword but that is an other matter of thing...
Zoidberg and Fizz
Claptrap from borderlands.
Blitzcrank/Claptrap combo OP!
Oliver from Ni No Kuni would wind up being friends with Annie.
My pick is Kratos from God of War I mean really The meta wouldnt even exist anymore He would be the best champs abilities mixed together. Think about it 
. I feel Kratos would be friends with or bond with because is from Sparta and is a Spartan Soldier being Kratos the Ghost of Sparta
Come on! who DOSNT want to play Link? closest to him is talon. or..... give him a Link costume.
Lich King and Illidan from Warcraft. Lich King would ally with Lissandra and Illidan would bond with Noxus.
Dragonborn from Skyrim.
He would bond with Shyvanna. Kinda. Sorta. Not really. If by bond you mean "Continuously try to take her soul.", then sure.
Giantdad from Dark souls.
Optimal build would prob be 
Samus Aran. But she doesn't just bond with a champion, her secret identity is one! She trades her Varia suit for a hunter's garb, wields a hand crossbow in place of her arm cannon, and picks up a small ballista instead of missiles! And she wears sunglasses because she's cool like that.
Tiny Tina from Borderlands 2.
She would probably have a connection with 
. Nuff said.
same with Fawful from M&LRPG
And Blackbeard(i'm not sure if it is.) from AC4.
with 
Crash Bandicoot and he will obviously bond with Ziggs.
Saxton Hale from TF2 would definitely bond with 
.
