Raizen Reborn

After her sister Luna soul was sealed. Grave started work on one his necromancy experiments. He extracted Raizens essence from his old sword and from his soul ending the fusion but keeping his power intact for himself. He then held a tournament for the strongest demons in hell but it was a trap as he captured them and combined them using necromancy into a new body fusing them with Raizens soul ressurrecting Raizen.

A side effect of the experiemt was that all the demons souls that Grave extracted from them were left unused so he infused Raizens soul with theirs creating InuTaisho the alter ego and dominant half of Raizen. Though weaker than Raizen this alter ego is much more ruthless and sadistic making him just as dangerous as Raizen, his true self.