Tekken 6

Just play 30 matches online. Just make sure not to quit early. You can create a session with a friend and set it to 2 rounds if you want to get it quicker.

Here is what I did with a boosting partner.
I created a session with 2 rounds, time limit at 60 since it doesn't matter, max players at 2, and a private slot for my partner. I invited him to the game and we both were ready. We then selected our fighters and alternated wins. Both of us had 30 matches within 45 minutes. We could of been faster if we were paying more attention to being ready.

If you boost these wins, make sure you are quick with being ready and skipping the countdown, this achievement could be obtained within 30 minutes. Remember to make sure you partner is always accepting the challenge or you will have to wait 20 seconds, making it take longer for the matches. Just keep selecting the same character, for example, I chose Hwoarang, and my partner picked Raven. This way you can quickly get to the fight and waste as little time as possible. If you don't want to alternate wins, like my partner and I did, just have the loser constantly walk towards the one that is winning.

With these hints, you could have all the online achievements done within an hour.

Good Luck!

I ended up playing about 20 or so matches altogether before I finally got a ranked win. with about 10 left I came to the conclusion all you have to do is hit A to start matches. So if you have it handy and want to get these out of the way. Plug in your Turbo controller and set it to A. Go do something else, come back later and you'll have your matches played.