Minchan is stuck in a dream-like state that features this mysterious best friend who can also see spirits but gets horribly abused by his dad to the point that Minchan becomes his reason for living. This seems to be a theme: some guy goes astray due to parental trauma, Minchan finds them and “sees” them, and they become obsessed.
His grandma features here, and I think that is a piece of her actual soul. That guy with the yellow eyes… Gweonreum or something? Was talking with Minchan’s grandma’s soul and saying that something “would make Minchan happy”. I’m guessing this experience is what he was referring to.
Don’t know much beyond that. Other than that Bihwan comes to his rescue.