Sorry for double post but I just found out Kratos is Sweet Tooth rival goddamn! Here's the full list:

Heihachi – Toro (weird)

Nariko – Dante  (makes sense)

Radec – Sir Daniel (Why?)

Kratos – Sweet Tooth (Both are psychopaths)

Jak/Daxter – Ratchet/Clank (Makes complete sense)

Nathan Drake – Sly (both thiefs)

Big Daddy – Sackboy (?)

Cole – Raiden (There can only be one)

PaRappa – Spike (Cause Spike hunt animals maybe?)

Evil Cole - Fat princess (I have no idea)

my explanations are

evil cole vs Fatty P: evil vs a bundle of joy and optimism...and cake. Lolz galore

Radec vs Sir Dan- Something to do with honor I'm sure...super serious army guy against clumsy skeleton knight

Heiachi vs Toro: japanese

Big Daddy vs Sackboy- story is lil sis have told big daddy that Sackboy is cuter..which ticks of Big D...no I'm not joking

Radec and Sir Daniel are rivals because SCE Cambridge Studio (makers of MediEVil) now work with Guerilla Games. Essentially they joined forces so i'm guessing that's why they made them rivals. Big Daddy and Sackboy because why the fuck not?! the first and last one idk I guess they just ran out of ideas and just made rivals with whoever was left.

Mugen I like your idea about Toro and Heihachi being both japanese and Radec and Sir Daniel could be honor and rank since they are both basically soldiers.

What does characters being rivals do exactly?

I think it's sort of like a story mode. Each rivalry has a reasoning behind it (which i'm sure is explained in the game). 

yeah the mines are really useful and that shotgun builds tons of ap

i would preorder if i could but i can't in my country :(

sucks because i won't get the preorder costumes which look awesome imo

Arcade mode something or whatever.

Here is toro and Heihachi rival cutscene.

http://www.youtube.com/watch?v=KY2XsFAq2KQ

Ok, wow. Had forgotten the beta released until last night. I have to admit that, although I was excited for this game, and really hoped it would be good, I had a bad feeling that it was gonna end up sucking.

BUT...after playing the beta last night I am now officially hyped! This game is really smooth, and is a blast to play. I meant to play just 1-2 rounds bc it was already really late (i.e. 5am), but I ended up playing for like 2 hrs. I played with only Sly the whole time. The more comfortable I got with Sly's moves, the more fun I had bc of being able to string together moves into combos.

The fact that I had so much fun playing this game is most impressive bc I'm a gamer who has pretty much zero interest in fighting games. I just don't enjoy them. And I've played SSB before (even just recently with a friend), and I'm not into those games either. Yet, I had a ton of fun with PSAS playing against only 6 of the 20 characters in the roster, only using one character thus far (Sly), having only a single game mode available, not having a chance to play locally with a friend/friends, and without being able to even touch the campaign.

PSAS is way better than what I was even hoping it would be. I will be officially buying this. Will be the first fighting game I've ever bought methinks. Hopefully a P.A. job makes me an offer sometime soon so I'll have the money to be able to pre-order it:/