At Adrian's words, the flaming eyes of King Yama suddenly burned brightly for a moment before fizzling out. One would think that a promise would be useless for a powerful god as King Yama, but he knows how powerful the Champion chosen by the Twin Gods is. A promise to deliver the soul of a primordial divine beast fused with a distorted god is not something King Yama could ignore.
If King Yama were to ever get that soul, then he would no longer need to endure the pain of losing all of his power for a long time. He would not need to reincarnate for a long time which means he will be able to fix all of the things lacking in the eastern underworld. He could even take care of the small and trivial squabbles that the other gods are doing.
"A promise is not solid enough for me to help you. What can you give me as a guarantee should you be unable to keep your promise? King Yama asked.
