All you need is a token, I use the Crown token from the Dragon expansion.

Everytime a character claims to attack in PVP, it immediately gains the "Courage token". There is only 1 Courage token.

The character with the Courage token adds 1 in Strength/Craft during attacks.

In terms of gameplay this means more PVP and more attention to the position of other characters.

Sounds like a good revealed ending to encourage more PVP. Should be fine if all players agree before play.