2(Harry Potter)

An Au where when the founders created Hogwarts, their wishes to teach and make sure witch/wizard/etc children would learn and be well taken care of made the castle become sentient but for many years only the founders and a few students/teachers knew about it.

Tom Riddle did not become Voldemort, he was forcibly taken to a unknown part of Hogwarts were he met a few adults(and the founder paintings) that explained to him why he was there and they would not let him go back to a place were he was abused besides trying to find a way to take the curse he got from his mother using a love potion to be with his father.

Voldemort still exists but he had no connection to Tom Riddle/Slytherin/Hogwarts/etc despite what Albus and others believe.

During the marauders era, Sirius, Regulus and Severus(plus some others) were also taken to the unknown part of Hogwarts were they also learnt the truth and were given to Tom Riddle and other adults who would be their new guardians so they wouldn't have to return to their abusive houses(so no bullying, just real pranks that make even the victim laugh because if a prank doesn't make a victim actual laugh then it is not a prank but bullying).

James and Lily still die at the hands of Voldemort(Severus wasn't the one to tell him about the prophecy and Peter wasn't the traitor, they hide themselves but not under a fidelius charm) so Harry is still taken to Petunia who while not abusive is neglectful towards him so Hogwarts takes him in as it does others from his year.

Albus does not know about this, he has always been so focused on his goals that he had no idea that his brother(and his sister would have too) was one of those Hogwarts took as her own and that many students ended up in Hogwarts care because of his neglectfulness and how he puts children in danger(because how can people say Hogwarts is the best school and the most protected one when he lets trolls and all that enter it?).

This idea probably doesn't make sense or needs to be deepened but I will leave that for someone who decides to write it.