Starts at yr 4 in the TWT. Context of previous years: In this 'universe', Harry, altough sorted to Gryffindor, is alone, excepts perhaps doing small talk with the lonely 3rd year Ravenclaw, who seems to be as bullied as him. On yr 1 Harry tried to befriend Ron and Hermione, however after the detention due to the dragon and the loss of points, Ron is much harsher with Harry, and him ends up distancing, having too vivids memories of his time at the Dursley's with Ron attitude. Hermione bowed to peer pressure, and she, too, distanced from Harry, and Harry having zero trust, decides to drop Hermione friendship altogether. Thus, all of the canon adventures up to 4th year end up with him alone.
For first year, he ends up finding the reason of the forbidden corridor, and since he can't rely on Hermione to study, he ends up doing a lot of it by himself, having dropped Quidditch due to the behavior of the House. Confrontation at the end is same, except Harry resolves the gauntlet with some street smarts too (ex. instead of doing the chess match, he goes back for a broom and uses it to cross)
Second year, with how school (and House) turns on him, validates his opinion on better being alone. He ends up in the CoS after stumbling by accident, hiding from students, and finds Ginnymort just about to summon basilisk again. Same fight happens again, altough it was much earlies than the canon fight date.
Third year, he sneaks away for Hogsmeade, ends up finding Sirius, having noticed the dog acted way too different to a normal one. Finds things from him, and Harry ends up getting Scabbers without anyone noticing, sends it to the Auror dept., but it ends up scaping very publicly, getting in front page of the Prophet, but Sirius is still wanted, going back to the Black Islands, since Harry told him to (and also since he doesn't completely trust him).
Now, on 4th year, having being dragged to the TWT, and again having the school turn on him, ends up finding about the dragons after seeing fire from the astronomy tower one night. First task was pretty much the same.
Fast forward to yule ball, he ends up going stag, not wanting to drag anyone to be a target, of course this also has repercussions, either Dumbledore's Frown/dissapointed stare ™️ or McGonagall's Look No.5 ™️
On the second task, he ends up finding a fake replica of his photo album as 'treasure', but also finds Gabrielle and same as canon, rescues her, unaware that security measures weren't enough, and was in risk of drowning, and so, after rescuing her, ends up with a life debt over a veela.
Due to said life debt, the day after, Delacour's parents corner Harry at some empty classroom, and ask him what he wants as repayment, explaining that veela's life debt are different from wizardkind, due to magical nature of the veela. Harry, as usual, tries to push it away / it was the right thing to do / etc., but parents insist, at which, Harry ends up telling/yelling/etc that they can't help him with what he wants.
As the parents wonder what Harry meant, and ask him so, Harry says that he wants a life free from abuse ("family", school, etc.), not having to constantly fight for his life, or fight against creatures no one else does, and also getting out of the TWT, since it involves all previous points mentioned.
After saying his piece, Harry is about to walk away from them, when magic reacts and he starts glowing, Delacour's having to shield their eyes. After glow finishes, Harry ends up transformed into a girl that looks like a younger Fleur. Delacour's parents pierce together that magic decided that repayment for life debt is making him their offspring, and since offsprings are girls, well, Harry gets changed. With that, he ends up with a new family, new school (uniform changed to Beauxbaton's), etc.
Thus, Harry has to learn to live her new life