Huuuh that’s an interesting question. I’m gonna take this question as what their main conflict and resolution would be like.
In this au, the reason Rinne doesnt want to go back home is because he realizes that even if he did become a good lawyer who can represent his village, going back won’t do them any good because right now, the system as it is is stacked against their favor. And so, he finds it better to stay and figure out how to make changes from there. This is something that Hiiro has to understand: the law in the end was written by humans, and humans’ perception of justice is subjective. There is no black and white.
I had a thought of Hiiro actually being arrested and Rinne has to defend him. Hiiro, though, believes he’s guilty because the evidence points to him, but Rinne knows he’s been set up.

OMG HIII thank you for being interested hehe 🥺
I THOUGHT ABT THIS A LOT i feel like rinne would be avoiding that scenario as much as possible, but unfortunately for him it’s far too easy to create a situation where he ends up against hiiro
I think it’d be funny if Hiiro, though across from him in court, would express his awe when Rinne manages to suss out inconsistencies and odd details most people would let fly over their heads. But I also imagined a running gag where after Hiiro compliments him, there’s always a ‘but’. I also imagined that if Rinne blundered, Hiiro’s line would be something along the lines of being disappointed and that he cant believe he waited years just to hear his Nii-san grasp at straws 😭 and i think hiiro would often do that thing where he imposes greater penalties when Rinne’s about to propose a theory or present evidence (like w/ phoenix and franziska) but not to spite him LOL it’s a display of belief in him if that makes sense
Rinne would be less than enthusiastic… hes proud of hiiro of course but theres a reason he didnt wanna meet… theres only so much pressure the man can handle

I JUST SAW THIS SORRY!!!
Omg the idea of a df investigations game is so cute. I myself havent played aai yet but id love to someday (in a definitely legal manner!!!)
Ngl his backstory in enst can easily pass as belonging to an aa character’s, so he’s pretty much almost the same. Note tho im not too familiar with madara’s chara so this is based on my limited knowledge:
He’s eccentric and outgoing on the surface, and can sometimes be akin to a horse thats been set loose. In this au, his arrangement with Kohaku has three benefits.
1. Workload can be split and they can be more efficient, given that they work together.
2. Madara can have Kohaku’s back, and if something bad happens to him that could sour relations between the Oukawas and the cops, he can be used as a scapegoat (oops)
2. Kohaku can reign in Madara, because even tho he’s a valued member of criminal affairs he’s still prone to… [hand gestures] not playing by the rules.
It’s like mutual babysitting LOL he still maintains his cheerful demeanor but definitely has some secrets he keeps locked away… i feel like kohaku would pick up early on that madara only lets people know what he needs them to know, including him, despite being partners