Picture the typical sports manga: Main character is untalented initially, but genuinely enjoys the sport they want to be a part of, and will work hard to make it to the top!! Their main rival is an arrogant bully (but the protag might be oblivious to this) who wants to beat down the main character and show them their place because of some serious personal issues. The bad guy is also extremely talented, and find the sport so easy that it's boring.

Now flip that whole thing upside down. There you go, it's Teppuu. You are rooting for a total jerk. The antagonist is an alright girl. Run with it.

I am no expert in MMA, but the martial arts I've seen come off as realistic with the occasional break from probable done for rule of cool.