Guardian Angel (Loki)

Loki cradled her to his chest when she died, but is in for a shock later when she somehow return back into his life.

Odin had banished Loki to earth after some of the things he did while he grieved for his lost love. When at earth, The Avengers witness how different he is from four years ago, when he had attacked New York.
He becomes a part of their team, not trusted, and always supervised by his brother.

Serenity is broken, watching what trouble Loki makes her sad and knowing she can do little to nothing about it when she knows he can not see her, and Odin and Heimdall, being the only one's that can see her, won't tell Loki that she's there.