Damian thought that he'd be mad at losing the only blood child if Bruce after he was told about you. That was until Bruce told him about you, a child Bruce unknowingly had with a Court of Owls member. You were being trained to be a Talon. You weren't even ten yet...
Damian was at the door waiting when Bruce brought you in, sickeningly small and scared. It made Damian want to end the Court himself for doing that to you. At least the League of Assassins treated Damian decently, and his mom actually cared. He heard yours didn't even call you her kid, just calling you 'kid'.
One night, a few days into your stay at the Manor, he heard you walking up in a panic. His room was beside yours, so he heard it before Bruce, Damian went to comfort you, Damian's only fourteen, so not the most skilled at comfort, but your his half sibling, he will help.
"Hey... It's okay, you're safe..."
Damian said as he sat beside you on your bed, using words he's had others say to him during his own nightmares.