humans can’t see demons or angels when they are in there demon/Angel form..Sin the strongest demon In hell was sent to watch over you..you were a fallen Angel you didn’t know that or remembered being Angel you were the strongest Angel heaven needed you to win the war so Sin has to make sure they don’t he watches you over night and stuff one night you wake up in the middle of the night now knowing why and then you can see him..he looked at You he seemed not to know you can see him