no actually you know what? i'm thinking that the whole joke of 'Damian calls Jason his younger brother because Jason's age reset in the pit' is very very good. but i want more.
Damian will die on the hill that Jason Peter Todd is his son, and he takes no arguments on the matter.
listen i just really like those AU's where Jason is practically comatose/zombie-like when he first comes out of the pit, especially when Talia then assigns him as Damian’s protector because the only muscle-memory instinct Jason keeps is 'protect those smaller than him', because i really like the dynamic of Damian then having to be the one that takes up the mantle of helping Jason with everything he doesn't remember how to do.
Damian spends all day every day with Jason at his side. he washes Jason, dresses him, teaches him how to walk and move again, to speak and communicate, write and draw; and because Jason is Damian's bodyguard, he follows Damian around like a lost puppy. to Jason he's just slowly coming back to himself as a person while doing his job by protecting this kid--but Talia never told Damian that Jason was his protector, she just told Damian to keep Jason alive. And so everything Jason does, in Damian's mind (especially with the added context of Damian teaching him how to be alive again) is the actions of a vulnerable being looking to their guardian out of comfort. and of course, nobody else would fit the bill of guardian but Damian, the person who is practically raising Jason from re-birth.
Jason follows Damian around the compound because he knows he needs to protect Damian--Damian sees this as Jason wandering around after the only person he feels safe with, the person who looks after him, his guardian.
Jason watches over Damian while he trains with his tutors--Damian knows it must be scary for a child to be left alone in a place such as the compound; it's only natural for Jason to prefer watching his father train than be alone.
Jason takes care of Damian, ensuring he eats and sleeps--well Damian raised Jason by doing those same things, it's only natural that his child pick up on the only love language he is exposed to, trying to turn it onto his parent.
it goes on and on and on; everything Jason does with the mindset of looking after his new baby brother, Damian takes as a son showing appreciation for his father. it takes like. a solid six months for Jason to be self aware enough to clock that Damian is literally calling him 'son' and 'my child' and by then it's too late. Damian absolutely will not let it go.
i imagine it's one of those things where like, Jason tried to argue it at first but Damian was really insistent, and eventually Jason gave up because it was like 'what the hell, it's not like the kid has much that sparks joy in his life anyway, might as well give him this' and starts ignoring it, letting it happen. and then after a while he realises how much it seems to agitate Talia and Ra's and the whole thing becomes kinda funny so he starts calling Damian 'dad' and 'old man' and this delights Damian which encourages him even further and the whole thing just kinda ends up being one of those jokes that you go along with for so long that it's not even that funny anymore and you just do it out of instinct.
like--to be clear Jason is still the mental guardian figure out of the two of them, and he takes care of Damian. it's just that Damian's in complete denial about this and instead chooses to believe it's the other way around, which Jason lets him believe because it's kinda funny to watch peoples reaction to it. like at dinner, when one of the servants will bring out some kind of dessert and Jason will just turn to Damian and go 'can i have dessert now?' and Damian will look at his plate and say 'finish your potatoes' and Jason will sigh before listening. to Damian this is normal, and he does this because of course Jason would look to him for permission, that's his child; meanwhile Jason is watching Talia stare at them both across the table like she's about to call a fucking exorcist and internally he is just Busting The Fuck Up just waiting for the moment Damian decides it's his bedtime.
i also just wanna point out how funny this would be in Gotham, when Bruce takes in his biological son who for some reason seems to HATE him but refuses to say why and after a couple months of Damian treating him like dirt to the point where even Tim and Dick are confused he finally gets Damian to tell him what the fuck he did and Damian is just like 'you are the reason my son is in such mental pain.' and Bruce is just like.
"did mother not tell you you are a grandfather?"
"w- NO??? YOU'RE ELEVEN WHAT DO YOU MEAN YOU'RE A FATHER- ARE YOU OK?"
"of course. i consented to being my child's father from the beginning."
"ELEVEN YEAR OLDS AREN'T ALLOWED TO CONSENT TO THAT."
and Bruce is. having a fucking panic attack about the whole thing until eventually they run into Red Hood on patrol and Damian straight-faced tells him that this 200+ lbs clearly adult man is the grandson in question and he just fucking. mentally checks out for about 20 minutes.
for the record Jason has never been so excited in his life. he fully intends on coming around the manor in-mask twice a week from now on just so he can call Bruce 'grandfather' and Dick 'uncle' while they stare at him like he's the fucking predator from Predator.
meanwhile Tim found Jason's 'baby book' under Damian's bed like a week ago which is comprised of just photos of Jason at sixteen years old, identity visible clear as day, doing shit like training, trying to figure out how to use the stove, practicing spelling, throwing spit balls at Ra’s; all taken by seven year old Damian that are marked as 'my son's first year <3', and he was genuinely so fucking baffled about how the fuck things could have spiralled to this specific point that he's just decided to go along with it and pretend he doesn't know. that is not his fucking circus, keep those monkeys away from him.