Gakuen-adjacent au where Ace and Ichiji are secretly dating (why secretly? Because of Judge, ofc), and they're pretty good at keeping it secret, always making sure to never be seen together on their dates, not even taking photos together or where the other’s face is visible, it helps that they're in different schools (Ace is in the public Shinsekai Highschool while Ichiji is in the private Germa Highschool) and they have the best help they could ever ask for: Deuce, who is always helping cover and both create and corroborate Ace's alibis. To the point that most everyone that knows them (or knows of them) thinks that he and Ace are dating (although they don't pressure Deuce to admit to admit their relationship - Ace is seemingly completely oblivious to all of this, especially since no-one asks or tells them anything about it directly and Deuce hasn't had the opportunity to tell Ace either).
This is a problem, however, because they're definitely not dating and Deuce actually has a boyfriend of his own (Shuraiya Bascud, whom he has told about the situation, thankfully). So, when Deuce is caught with his actual boyfriend, people are appalled that he's cheat on Ace. Deuce, of course, tries to defend himself, but no-one really believes him. And now the whole student body thinks Deuce is cheating on Ace.
This does end up getting to Ace, who tries to clear the air.
Ace: What? I'm not dating Deuce?
Student: Yeah, he doesn't deserve you! Good for you for leaving his sorry ass!
Ace: I WASN’T DATING HIS SORRY ASS TO BEGIN WITH
Student: Exactly, you’re too good for him!
Cue Ace insisting he actually has a boyfriend with whom he has been for a good while now, unfortunately, he lacks the proof and no-one believes him. And, this time, Deuce (the only true victim in this whole fiasco) refuses to be of any help. So now the whole student body thinks Ace is in some kind of denial delusion or something like it with his imaginary boyfriend.
???: Look, Ace, I want to believe you, I promise, but there's more proof against you than in your favour.
Until he and Ichiji are finally caught (Judge has finally been dealt with, which is completely unrelated to everything going on Ace's life) when Ichiji arrives looking for Ace (with the good news) and can't resist giving him a hug and a kiss on the cheek (no thoughts on the crowd since he's now free from Judge and can do whatever the fuck he wants, finally).
Students: omg Ace, how/where did you bag that baddie?/it's good to see you've upgraded
Ichiji, who has absolutely no idea of anything that has been going on with the misunderstandings regarding Ace and Deuce: We've been dating for years now
(Sanji watched all this drama happen in real time and stayed quiet for Ichiji's sake and - mostly - to not get involved in that mess. Same as Luffy, who only really talks about it with his boyfriend, Law. Although, in all honestly, even the few who knew the truth also wouldn't have been believed if they spoke up.)
All the while, Yonji and Niji have been snooping little shits investigating Ichiji's secret relationship and his delinquent-looking boyfriend (with Reiju having been the one covering for Ichiji), which is how they met Sabo and Yamato, who accidentally distracted them from their original mission.
In Yonji's case, he fell face first fro Sabo after watching him and the R.A. dealing with some actual delinquents, so Yonji changed his investigative objective from Ace to the revs and became a regular at the Baltigo cafe where Sabo works, unintentionally befriending him (and later helping him take down Judge).
Niji, however, dragged Yamato into his own snooping, continually getting distracted by Yamato’s chattering and accidental turning of their spy-dates into actual dates (it takes Niji a bit to admit his feelings but he does end up doing so).
(and thank you @cherry-mash for bouncing ideas with me so often!!!!)