The soul, which during the process has also completely digested the essence, which made his dark properties increase.
This process of creating his body and soul took longer than he expected but it was obvious creating a body was hard. If not for his talent, he wouldn't have been able to do this feat.
But since he had already done it at second-tier his road to comprehending the death rune would be much smoother.
He wouldn't even be surprised if he comprehended the rune in an hour. Finally moving his body, he could hear the 'chik, chaks' coming out from his body whenever he moved.
This was normal as his new body was created just recently.
As for why he didn't add any extra limb or anything, this time his whole body was convertible, this time he didn't depend on it to survive, instead it could be said to be the container for his soul.