@Katz- I never played that game but I've seen that character all over the place. In fact I think I saw him in person, can you double check for me?
@DM- Maybe Heihachi finally got access the devil gene? I always thought it was weird that he seemed to be the only male in the family who didn't have that power(even Jinpachi seemed more supernatural than him). Could explain his regression. Or they just don't wanna kill off Heihachi so they mangled the story to shoe horn him in.