..

I haven't read the novel but from what I've read from spoilers and stuffs, the reason he "disappeared" was his powers was too much for Earth that he either need to leave or let Earth bear the consequence of something (idk but maybe destruction???)

I read spoiler too years ago, but I don't read that part yet
So our Hyunjae is the most powerful S class on earth?
Wow what a perfect Male lead lol
(￣∇￣")

That's what I infer from that spoiler too, since Hyunjae is also above the keyword which worked on Hyuna easily