@Anime fan my theory is quite similar but I think the hyung reincarnated (maybe at the same time, but i think wayyy earlier than mc) as vael w/o knowing about navi, hence why he "grew closer" rather than already having a prior attachment. 
-- would b cute since that could also means he feel for him twice 
so many yet so few..
why is my bl pool drying up ( ´⊇｀)
why is my bl pool drying up ( ´⊇｀)