Thinking about more Dadsley adopting Diona
Dude becomes a fucking surveillance camera to make sure Diona is safe, cause he KNOWS there are rapists and pedophile in the Fortress that would happily take advantage of her, so he would probably have her wear some kind of tracking system out of (reasonable) paranoia.
The other inmates (minor criminals) actually start to like Diona and start treating her well, and even Wolsey decides that she gets the better welfare meals. Like, she still has to pick a straw for her meal, but she doesn't get the bad ones anymore.
Wriothesley teaching Diona how to fight in hand to hand combate while Diona teaches him or gives random tips about hunting. I like to imagine Diona accidentally punching him in the nuts during one of their spars and he collapses to the ground groaning in pain while Diona panics. Sigewienne is just laughing the background.
Wriothesley seeing Diona getting harassed by an inmate, and before he can intervene, she just straight up decks him in the balls like she did to Wrio during their last spar before walking away, and he can't help but cry from being so proud of her.
Diona would definitely help out Sigewienne in the nurses office since she's a healer in the game, and Sigewienne would teach her better ways to heal people.
I think of the barret society was still there while Diona is there too, Dougier would definitely try to kidnap Diona and torture her into following him, and when Wriothesley inevitably finds out, he'd 100% torture Dougier in a much worse way. After comforting Diona, of course.
Wriothesley would send letters back to Mondstadt to let the authorities and/or her extended family know about what's happened, and once Diluc gets wind of it, he makes plans to fly over to Fontaine to check on her (because the knights can't even be trusted to do this), only for the residents of Springvale to come to him, asking if they can come with him or deliver letters for them.
When he arrives to Fontaine, he goes to Neuvillette and asks if he can see Diona, to witch he responds that "the Fortress of Meropide works independently from the Court of Fontaine, and I would usually suggest that the person asking to give up their endeavors. But given the unique circumstance of Miss Diona's case, and the Duke's relationship to her, I can at least send a letter to inform Wriothesley about your request "
Wriothesley accepts Diluc's request and he goes down to meet with Diona in his office, but when he gets there, it's just Wriothesley and no Diona in sight. Diluc starts getting defensive about the situation and start "subtly" demanding to know where she is. To which Wriothesley would respond with "she's here and will arrive shortly. I just wanted to prepare you in case she has a fit and runs out, considering how negatively she's talked about you."
Diona eventually comes in after Diluc and Wriothesley talk for a few minutes, and she's angry and defensive at first, but eventually apologizes about how she treated and talked to him, and Diluc says that he doesn't mind and understands why she said the things she did.
After the awkward greetings, Diona starts asking about Mondstadt and how her friends and extended family are doing, and Diluc gives honest replies, relieved that she seems to be at least safe within the Fortress.
Diluc hands over the small bag of letters from the residents of Springvale to Diona before leaving and waving goodbye, and Diona honestly starts to break down crying after he leaves from all the people that wrote to her. Wriothesley hugs and comforts her about it, happy that she has people who care about her (despite her shitty dad.)
Diluc and Wriothesley would definitely keep in contact, mostly to give Diluc updates about Diona, but also to try to get to know each other better. Wriothesley sends him tea from time to time, and Diluc send him grape juice.
Diona would definitely sneak past her curfew (cause Wriothesley would absolutely have one for her) just to see him fight in the Pankration Ring and kick serious ass. During one particularly challenging fight, he'd get hurt pretty bad, almost getting knocked out, and Diona screams to him "GET UP AND KICK HIS ASS, DAD!" without realizing it. After the fight, Wriothesley is stuck between scolding her for staying out late and crushing her in affection for calling him dad.
Diona denies ever calling him dad.