Every mission. Every battle. Every invasion. The Avengers see the same teenager sitting quietly in the corner, watching everything unfold. They never help. They never interfere. They never explain why they're there. And no matter how hard the team tries, they always disappear before anyone can get answers. At first, the Avengers think it's a coincidence. Then they think it's a mystery. Then they witness the kid casually stop a collapsing building from crushing hundreds of people. And suddenly the mystery becomes a lot more complicated. Especially when Thor takes one look at the strange teenager and greets them like an old friend. Because apparently the most powerful being the Avengers have ever encountered isn't interested in ruling the world. They're just here to watch. And they're having a great time.