Stunning Assassin

Derek stood there, silenced by the confusion and turmoil flooding his mind. He had come to this world believing he had a purpose, but now he felt like that purpose had been stripped away, leaving him with nothing but emptiness.

What is he supposed to do? Kill Rakuzen and consume him?

Even if Derek wished to do that, there was a very high possibility he would fail. In fact, should he get outside help, their chances of failure would remain high and that's the reason why Sol was created. 

He was the only one capable of matching Rakuzen in power, which is only if he is ready to put his life on the line and die giving it his all. His victory isn't even guaranteed.

Why would someone this powerful need the protection of a lesser being like himself?

"You overthink things. " Sol said with a light chuckle. "The true purpose of our visit to this world will be revealed in time." He added.