Your gateway to endless inspiration
AKA "Damian thinks flirting/dating entails a lot more violence than the average person and Danny's confused as to why this vigilante keeps prepositioning him for battles" idea!
Okay, so, I know Damian went to live with Bruce when he was still a kid, 10 or something, but what if he joined the Batfam when he was older? Like imagine he's had an entire childhood and adolescence in the League of Assassins, so he's raised in this culture of being The Best (i.e., strongest fighter, intelligent and knowledgeable, etc.). And maybe the LoA typically follows the tradition of arranged marriages, but you may court someone if they're seen as an equal. Talia with Bruce, for example. And!! It's not courting like the "sweet serenading, fan-fluttering, going for a walk in a park with a chaperone" Bridgerton-type courting.
In the League of Assassins, you court by battling your intended's guardian to the death.
So, fast-forward to Damian learning how to assimilate into Gotham city culture. He still struggles to learn his place in the Batfam, but he's older and has a better grasp on his emotions; no trying to kill Tim, no constant threats of death and dismemberment, no jealously protecting the title of Heir. He's... kind of like Bruce actually. Damian is scarily competent, logical, and level-headed but super intense.
Danny, who's been living in Gotham for awhile and has gotten to know the Batfam fairly well, meets the newest addition while on patrol. Let's say he's still Phantom but cosplays as a Meta. Bruce let him stay in Gotham because he's a sucker for a black-haired, blue-eyed, abused kids.
Their introduction goes about as well as the Batfam expects. Damian is all business, only offering a quick nod and his name before returning his focus to patrol. Danny's maybe a bit taken aback but doesn't take it too personally since he'd already been given the rundown by Tim.
Damian and Danny end up patrolling together while Batman and Cass investigate some lead by the docks or something. Their night turns pretty badly when Clayface attacks. Damian ends up being the damsel in distress since he's only ever faced human enemies; even the deadliest opponents in the League could still be killed using swords or the usual combat weapons. Danny ends up using his powers to defeat Clayface before Batman can come back.
And then Danny goes home, content that he was able to let loose a little without Batman there to supervise him, and doesn't think about it after. Damian, however, is downright enamored because Danny was terrifying while fighting. His movements were lupine like a panther, a comfortability in his posture that spoke of decades in combat; his eyes turned Lazarus Pit green, chilling in its intensity. His skin took on a ghostly pallor and Damian could've sworn his teeth sharpened. He looked like a deity of War.
(Danny doesn't know this, of course; he was just happy to enjoy a really good fight since he hasn't unleased his Full Ghost powers in a long minute.)
A couple weeks pass and Danny's invited to a Wayne family dinner. Except when he shows up, Damian - who he thought he'd kind of bonded with since he'd literally saved the guy from Clayface - tries to kill him. Straight up: full assassin regalia, recently polished sword, genuinely throwing his all into the battle.
The Batfam try to intervene but Damian easily (and painfully, as Jason was flipped face-first into a table, Steph was stabbed, Dick broke his elbow) fought off. In the end, it was Danny who froze Damian and yelped a frazzled, "What the fuck, dude?" Bruce agreed to dethaw his son if he never, ever drew his sword at the dinner table again and explained why in the world he randomly attacked Danny unprompted.
Except Damian's response is to apologize and formally proposition Danny to a "battle to rights"... and the Batfam are all like, wtf?? What is that?? They're thinking maybe the rights to the Wayne inheritance, but Danny was never adopted by Bruce (he'd had enough of millionaires trying to adopt him so he'd politely declined all the Batfam's attempts to rope him into the family; Dick, Babs, and Jason of all people included).
The thing is that Danny's parents disowned him, he doesn't consider Vlad to be his guardian, and Jazz isn't really in the picture here. Bruce isn't considered his adopted father figure, either. So, Damian concluded the next reasonable course of action was to fight Danny for his right to marry him.
Cue months of hilarious misunderstandings where the Batfam try to keep Damian separated from Danny since he keeps trying to fight him... and worse, is that Damian loses every damn fight. Danny has non-human powers and endless knowledge of dead languages, cultures, space, history, etc. Damian likes him so, so much but he can't win the battle to rights and it's driving him insane!! He calls his mother to vent his frustrations and she only encourages him, tells him that he shouldn't want to marry someone he can beat so easily, that he picked his intended well.
It gets to the point where Damian's trying to use any and all knowledge of Danny's weaknesses. It just makes him more obsessed because there doesn't seem to be any (there are, but they aren't on Earth and/or are locked down in the Fenton Works labs, untraceable to anyone not in the GIW).
And Danny's just like, what the hell!! Why the hell is this guy targeting him over and over again? The worst part is that Damian is actually very intelligent and thoughtful - during their duels, they quip back and forth in ancient languages, discuss thought-proving topics, and when Danny beats him, they have a quiet moment to compliment each other's fighting styles. They discuss ancient history and art together. Damian is one of the few people who can actually match Danny's odd tidbits of random knowledge, as he'd been extensively educated while in the LoA.
Finally, Danny just asks, "Why do you keep trying to fight me?? Do you just hate me or something??" (He hopes not. Danny's starting to like Damian a bit too much, especially after their fights when Damian offers to cook him some of Alfred's most popular recipes. Danny's a terrible cook so he actually looks forward to having a surprisingly good meal, sans the attempted poisoning at times.)
And Damian just... stops. He's utterly flabbergasted and perhaps a little bit exasperated since it's been months of being unable to win the battle to rights. "Why would I request to court you if I hate you, habibi?"
Danny's like, "Huh???"
Damian explains how courting works in the LoA and why it's been on-sight ever since the Clayface fight. And everything just clicks for Danny!! He's also kind of... flattered? Like, he's never been wanted so badly that someone would fight to the death for him (Danny's just like "he's confused but he's got the spirit!" about the whole "if Danny doesn't have a guardian, I'll just fight him instead" logic).
So, he's like, "Of course, I'll date you!!"
It'd probably be an adjustment period since Damian's idea of a romantic date is watching his boyfriend go Full Ghost on supervillains. He'd just be heart-eyeing at him the entire time. And it's not like Danny's not having a good time!! He just expected there'd be more date-night activities and less patrol-night activities. So, Danny introduces Damian to more "regular" hobbies, like going to the zoo, movie nights, bookshop dates, etc.
(another side idea in my head is Damian introducing Danny to Talia and Ra's al Ghul, like, "This is Danny Fenton, my intended." But Danny is decked out in his Ghost King attire, crown included, and introduces himself as King of Infinite Realms, Space, and the Dead. Meanwhile his boyfriend is just looking at him with this look of utter besotted lovesick pride. There's so much potential!!)