
He may not be a real goblin but his human body may be reacting more as a goblin than human at this point. Remember that Geumsun put those markings on his vitals to basically stop his body’s life flow. He doesn’t need food or sleep anymore and relies on yang energy as a goblin would. So although human, reaper blood and yang energy affects him as it would a goblin.

Hello I hope I am not too late! I’m often confused about this story too but I’m working hard on answering your questions~
It’s Yama’s fault that 704 feels guilty about San. Geumsun is also somewhat involved, though he didn’t knew that Yama would “frame” 704. Yama needed San to go to the underworld WHILE being alive, so his existence his completely erased from “earth”, hence Hwan’s memories too but needed SOMEONE to “accidentally” bring San to the underworld. (Pls lmk know if you want to know more about this point, since it’s another long explanation!)
Because of that, San isn’t really “human”. I once said he was something like schroedinger’s cat, not really “alive” but not really dead. His current state must be similar to what they call a “goblin” then. San doesn’t need to consume food, or sleep but he does need some sort of energy to stay alive, I’m guessing it’s 704’s reaper blood.
Please take it with a grain of salt. I hope I could help tho! ><
Um, is it San’s fault that 704 thought this whole thing was his fault or is that because of Yama? Because I don’t think San knew either... or did he????? Also if he is a human then um why tf did he like drinking 704’s blood?????? Wtf????????? Is he secretly a goblin???????? What is going on????????????????????????? Surely no human would like drinking a reaper’s blood even if they were low on yang energy, like what the actual fuck is happening