Ok, just got this with my buddy. You're going to want to pick Shura, and then pick a map where you can easily ring out, we did the River one where you're on a small platform going down stream (yes, I forgot the name). Then start up the game (be sure it's a ranked match) and run at your buddy and push him to the edge the while sprinting at him and he's near the edge, press Y, or Y+B and you'll do an Animation Grab on him and throw him off the edge...
Average Round Time: 4.5 Seconds.
Average Match Time: Under 30 Seconds (Damn Cut Scenes.)
Do this method and you'll have this (and the Level 20) in the bag.