I think this would probably be a Jango Survives AU where he ends up embroiled in Separatist command nonsense—he despises Ventress particularly and she wants to fuck that middle-aged man so bad she's unwell—probably because Dooku made veiled veiled threats against Boba, nothing actionable, just takes an interest in him and his training that Jango finds sinister so he takes up a reluctant General position in the C.I.S. This of course pushes the Death Watch to become an equally reluctant ally with the Republic because if there's one thing Pre Vizsla hates more than Jedi it's Jango fucking Fett. During a joint-operation with the G.A.R. and the Death Watch, Ahsoka gets captured by the Separatists/left behind by DW with a small squad of clones. Thus begins Jango being forced to watch a tiny Jedi child go absolutely feral at anyone who comes near her pathetic collection of defective clones, and she seems to have some kind of grudge against him in particular. Eventually the Jedi he captured on Geonosis stages a rescue mission and Jango ditches whatever the objective was to get the hell away from the angry young father who clearly wants to take his head off for imprisoning his foundling (or however Jedi do it). Which then kicks off a slowburn enemies-to-something spanning the whole wars which ends with Jango dumping evidence that Palpatine was playing both sides of the war to stay in power all over the holonet and then fucking off from all of this nonsense. Anakin shows up like eight months later, he has a therapist and doesn't have a lightsaber, and Jango agrees to his own therapist and one (1) date. (It turns into a three-night stand and they somehow end up married like a month later. Boba never lets them live it down.)
