You’ve always been a part of his life. Even when he was a newborn. He didn’t even know you existed. That was fine, you were simply meant to watch out for him. His mother; absolutely worried for his and safety, and therefore treaded into the forbidden area of sorcery or summoning shikigami that wasn’t from a technique. That’s what you were; the added task of watching over him. You’d follow him everywhere. However he’d caught you one day. Changing your size from a simple fairy to a human size.