The Demon's Protector
What if Jason never left the League of Assassins to get his revenge on Bruce? Jason gets captured before he can leave, just minutes after the Lazarus Pit restored him fully and is dragged in front of Ra's al Ghul. Instead of killing him, Ra's appoints him as his grandson and heir's Dark Angel. Jason is now the protector of Damian. He travels around the world, learning skills to aid him in defending Damian whilst also assessing their skills in teaching, so Damian can have the best of teachers.
He becomes the Red Hood, a ruthless killer with a 100% success rate and watches as Damian grows up, from an assassin to a Robin but never revealing himself to the boy he was sworn to protect; Damian never thinking that Jayjay, his friend from childhood, Jason Todd, his literature tutor and the Red Hood, one of the League's greatest assassins, were both the same person as well as his Dark Angel.