There's nothing believable about this. From the getgo, the fact that female fighters can stand toe to toe with equally trained male counterparts makes absolutely no sense. The fact that Akita's basic moves that he learns are able to win against long trained martial artists (like the karate salaryman) makes no sense. The fact that both of the guys in this chapter had no serious injuries after being pushed off a cliff makes no sense. There may not be any supernatural things involved in this, or superhuman per say either, but it's not exactly grounded in reality either. If you're looking for believability, then this manga isn't for you mate.