Some Explains

So
San was A human in the past . He was a human with strong spiritual sight and has a very strong mind which means that he can see ghosts.monstery ghosts, goblins. reapers, everything, it`s called he had the eyes of goblin.
-that explains why Hwan wanted to eat/hunt him. because Hwan was already weak cuz GS attacked him and needed some strong human to eat to keep his powers up,that why he was keeping an eye on San.which means if Hwan wanted to eat San he has to kill everyone next to San and that only his aunt.
-His aunt was also a spiritual person but not powerful as San. she can only feel spirits that why she has the Goblin Stone.to keep the spirits away from her.and that`s explains why the Goblin stone with San and he said he found it in an accident.
-Right now that explains why GS was always making sure if Hwan actually remembers San.because of the past. but the two can`t remember each other during the accident that happened in the past and also San has GS powers so it affect Hwan Sense.
-San was also learning archery that explains his body still remembers it from the past when he attack Hwan with it.
-704 was a Human before becoming a reaper , he has committed a huge sin. but not known until now.GS may known him when he was a human,that why he was shocked when he saw him and when a human became reaper he can`t remember his past human life,and yama known that, that`s why he used 704 to tell GS that he has a reason to attack Hwan now.