So after thinking about it more and looking at the responses in this thread, this is what I came up with:
-Desire for Victory [Counter Feat]:
Triggers whenever HP decreases or after losing a point. Mental permanently increases by 1. The third time Mental increases through this effect, activate Devil Mode.
This is a bit different from what we've been using in the past in that Mental increases instead of decreases, but this way it actually doesn't clash with Intense Concentration for a change. The HP part represents the provocation that has been brought up. Since not all Mental drop effects are a result of provocation, I think this is the best way to do it and he was hit in the face every single one of those times anyway.
Note that this is just a preliminary version and may change a bit in the future. For example, the HP condition might be removed depending on if there are any drops that aren't tied to winning the point.
Thanks for everyone's contributions so far.
The next character I would like some input on is Krauser. Like I mentioned before, SC will be made weaker, but this is about something else.
In Krauser's fanbook profile it says that his Stamina and Mental are only a 2 each because he overuses his KO shots. We normally don't force the player to use certain moves, but should we do so in this case? Or, if not, should Krauser have a feat that increases those stats if he's not using SC? What about if he's playing doubles with someone like Yanagi or Shiraishi?
@Above
I forgot to ask, but is this in relation to Fuwa and Hakamada specifically or do you have any other characters in mind that he beats but shouldn't?