His story was wrapped up between DMC1 and 3, he was only in 4 because the fans would've had a b****fit if he wasn't. That's why he's like he is in that game, he no longer has any purpose other than to d**** around. They should have just made the whole game about Nero, it would have ended up a lot better that way.
He barley had any role other than troll nero and the order of the sword organization. The only note worthy thing was caring about vergil's sword and accepting nero. It seems like he had more in the game but DMC4 is an unfinished game.They should have released DMC4 SE.