Have an angsty KHR AU (Playing fast and loose with flame lore and characterization. Also, I haven't figured out what the 10th Gen Guardians are doing during all this, but whatever it is, it involves So Many miscommunications.)
Tsuna doesn't want to be a mafia boss. He hates the violence, he hates the danger, he hates knowing that if he messes up, it can get people killed.
But no one really listens to him. Not even Reborn, who just sees Tsuna's whole "I don't want to be a mafia boss" thing as a sort of juvenile rebellion phase.
(But it's not. Every time one of Tsuna's people comes home hurt, every time Tsuna has to inflict harm on the battlefield, every time Tsuna is exposed to the casual cruelty of the underworld, it damages something inside of him. It scars his soul. He hates it. He does not want to be a mafia boss.)
And then Timoteo's health declines. (These next two paragraphs were heavily inspired by Break These Chains on Me by Luki on AO3.) Tsuna, knowing his time is running out and absolutely desperate, tries to make plans to get tf out. Maybe he signs up for civilian university. Maybe he makes plans to travel. Maybe he tries to create a fake identity to just run. And Tsuna, who has learned to rely on and trust Reborn -- after everything, how could he not -- confides in him about these plans.
And Reborn -- who has never really understood why Tsuna hates the mafia -- thinks this is one last (highly irritating) attempt at a teenage rebellion. It's not entirely unexpected, what with the weight of being Don Vongola looming over Tsuna's shoulders. And so, in a true Disappointed Reborn fashion, he responds with a harsh but effective lesson. He plays along with Tsuna's escape plans for a bit, and then. And then. It's the day Tsuna plans to vanish, and Reborn sits Tsuna down at the table, with Xanxus and Timoteo, and tells Tsuna if he doesn't fall in line Bad Things are gonna happen to his people.
(Reborn does not intend this to be an actual threat. It's supposed to be a slap on the wrist. A sort of, "Yeah, you're a teenager, but you need to start conducting yourself more seriously, knock it off before I actually get mad." Sure, Vongola is threatening to kidnap Tsuna's mom, but the kidnappers are just going to take her out for tea and cake and a spa night, and when Tsuna shows up to rescue her she'll be fine. The real punishment will be the physical path to go get her -- Reborn has an Embarrassing Obstacle Course TM planned.
And so on, for all of Tsuna's precious ones.
Reborn does not consider that Tsuna might actually believe the severity of the threats. After all they've been through, after all they've done for each other, Reborn knows Tsuna would never believe that Reborn could actually hurt Tsuna's people.)
But Tsuna. Well, Tsuna's on a different page. This life is killing him, slowly, and when Reborn tells him that he never intended to help Tsuna escape, it hits Tsuna like a full-on betrayal. And while mere minutes before, Tsuna knew that Reborn would never even dream of harming Tsuna's people, Tsuna no longer can trust this. Tsuna fully and absolutely believes that Reborn's threats are real, and that there will be permanent consequences if he doesn't comply.
Tsuna thought Reborn actually cared about him. Reborn had, slowly but inevitably, become something like a father to Tsuna. But in that moment, Tsuna realizes that he actually was just a job all along.
And Xanxus. Tsuna also thought Xanxus cared about him. He thought they had come to an understanding. He thought they were starting to become brothers, of a sort -- bonded by battle and trauma and shared responsibilities, by nights complaining to each other over dinner or over the phone. And as Tsuna sits across from them, hearing his people threatened and knowing he is, in fact, going to be forced to Italy, he comes to believe that none of that new brotherhood was real.
And Tsuna realizes he has no choice. He never had a choice. He will end up in Italy, as Don Vongola, no matter how much it is going to kill him inside.
And worse: the people he has come to love clearly do not love him back. If they did, they would not be doing this to him. And sitting at that kitchen table, seeing the disappointment in Reborn and Xanxus' eyes, he knows that he is never going to be enough.
But he knows, he knows, that he isn't going to survive Italy without having them in his life supporting him. Because even if they don't love him, he does, truly, love them.
And he comes to the conclusion that if he remains as he is -- weak, useless Tsuna -- not only will he inevitably lose them, but he just flat out won't survive the life stretching out (long, so long, and so so desolate) before him.
He images the mafia boss that they want him to be (as he perceives it). He thinks about all the characteristics they must want him to have, all the things they expect him to want, and he conjures an image of this better Tsuna in his mind. And then he harmonizes with it, becomes one with this false image of himself.
But it doesn't work, not all the way. There are still bits of him, the original, weak, disappointing Tsuna left. He can feel it, in the dread at the thought of the life before him. In the shocked-hurt he feels at this betrayal. In the agony of knowing that they don't care about him, they never cared about him, they only care about his title.
So he puts those bits of himself in ice.
And suddenly, the years ahead don't seem so bad. Suddenly, the betrayal seems reasonable -- after all, wasn't he acting so silly, so juvenile, trying to escape like that. Suddenly, it doesn't matter that they don't love him back -- of course they don't, why would they love him? -- all that matters is he loves them. As long as he keeps himself in check, and matches their expectations, nothing is wrong.
Tsuna looks at them, sitting across the table, and complies with their demands.
Reborn does, for a moment, think that it happens a bit too easily. There's none of the usual screeching, no dragging of the heels, no protests. Right then, Reborn fully expects it to boil over at some point in the future. (He thinks, maybe, that Tsuna is playing along now, but will have a teenagery-protest again as it gets closer to the time they leave for Italy.)
Reborn thinks, merely, that Tsuna has put on the mantle of maturity. It's a little ahead of schedule of what he was expecting, but then again, Tsuna has always exceeded expectations.
Time passes. Timoteo's health declines. He dies. Tsuna goes to Italy, and becomes a mafia boss.
(It's a golden age. Tsuna is just as compassionate and selfless and determined as Reborn always knew he would be. There is a peace, unlike anything the underworld has ever seen, because of his rule.
This peace is a result of the core of Tsuna peeking out. It always would have happened.)
It's five years into Tsuna's reign before people begin to realize that something is really, really wrong with Tsuna.
They do figure it out, eventually. And when they do, when they realize what happened and what caused it, it breaks them, just as much as they broke Tsuna all those years ago.
