Yeah he died when he got a bit older. That's why the angel said he didn't expect Kouki to be there so soon because he thought he would have to wait longer for him to get there.
Oohh!!!! TwT Thanks for the explanation. My thoughts went dark for a sec like "Did kouki kill himself to be with the angel? Didn't he move on and try to keep on living??" I'm glad it turns out he died a bit later in his life, and not just after the angel left ;w; This is such a good read!
Yeah I figured he was older since he has white hair at the end. It was so good I ended up tearing up ╥﹏╥
Wait im confusion... They met again in the extra??? Did Kouki... die? O.O