High school dxd: The Winter Soldier

The Winter Soldier is a deadly bounty hunter from the great war, not much is know about this man. Only the faction leaders know who this man is. When Rias is caught up with her battle against Riser to be a free woman, The king of hell will call upon the deadliest assassin alive. Will he help the devil king free his little sister or will his past with the devil faction make him watch this plan go up in flames?