The Boy Who Lived to be an Assassin's Protege

Odin Lowe thought it was going to just be a simple job, until he found Harry Potter of all people in a cupboard under the stairs, half-starved. He decides to take the boy in and teach him how to survive and kill. Harry never expected to be saved, until Odin kicked the door down. Heero-is-Harry fanfic. Sorta slow burn.