Prompt: Danny Fenton Todd
Jason is just chilling in a safe house at home when an ominous swirling green portal opens in the middle of his living room and several beings with giant eyeballs for heads pull a trussed up teen through.
Freaky eyeball: "Congratulations, revenant, you have been chosen to be the abom- I mean... the halfa's new guardian."
Jason: the fuck did he just call this kid?!
The eyeballs then promptly leave, the teen still trussed up in the middle of his living room. Jason unties the kid and sets about interrogating the kid because wtf. Jason finds out:
He has no family or home to return to
He is a half ghost and has all the ghost powers that come with that.
Jason had an older brother once, his name was Danny, he was 15 when he died. Jason looks at Danny: black hair, blue eyes, simmering rage, gaunt corpse-like features. Yeah, this could work.
"Roy! I need a favor. I need you to hire someone to dig up my brother's coffin and transport it out of Gotham and, this is important, it needs to be super obvious until it's out of Gotham. Then Batman needs to lose all trace. Got it? Good. Okay kid, you need to turn invisible and stay invisible while I go steal a plane."
Cut to Batfam PoV, where Jason suddenly leaves town with no explanation, then the next day his older brother's corpse gets stolen ("Jason had an older brother?!") which Bruce fears is a sign their IDs have been compromised. They try to figure out what's going on but the corpse trail goes cold outside Gotham and Jason isn't answering any calls. He's all over Eurasia, fighting all kinds of people, even ending up in a few LoA bases. He finally stops at Nanda Parbat (to intro Danny to the remnants of the All Caste, but the batfam doesn't know that) before stealing yet another plane and heading back to Gotham.
"Hey everyone, this is my big brother Danny. No, we will not be taking questions at this time. C'mon, Danny, I'm exhausted, let's go home."