Werewolf character?

Messing around in my head, I thought it would be real cool if you could create a sort of werewolf character by somehow making the game cause "Morph" status when they (and only they) get low o HP. I know there are relics that do that, but is there a way to make it character specific and not have to rely on equipment? If not possible, is there a way to get it done on non-relics? If not, is there a way to do this and prevent players from changing relics?