I Eat Tomatoes
Calm Sea is a classic antagonist. He's convinced that he's the important one & that his glorious destiny justifies any sacrifices made for his own advancement. You know, as long as other people are making the sacrifices. I fully expect that he will betray the human world at some point, quite possibly out of jealousy.
I actually understand where he's coming from. The progression of a genius is infinitely more important than the lives of a million mortals as callous as that may sound. As has been stated often, a single transcendental figure could immediately end the war while mortals have no real impact on the war. However, there's no way the demons would provide great cultivation methods considering King Calm Sea has been killing so many of them. I think it's pretty clear there's some sabotage involved in the cultivation methods based on the final line. He doesn't seem to be someone who doesn't care about humanity based on his thoughts in this chapter, so the demons are probably going to take control of his mind to make him fully betray humanity, leading to Meng Chuan's earlier vision. A Creation-level expert is normally practically invincible in the current human world, so I'd reckon the cultivation method has a backdoor to his mind to allow easy control.