Kenjaku asked him to kill that human and he was ready to do it, until he hears the human's words.

"Please, don't kill me or my brother will be alone!"

He freezes. He knows better than anyone else what it is to love his brother. And that's something really important to him.

"I won't kill you." He just says with his tired face. "Take care of your bro, okay? You shouldn't stay here, it's dangerous."