3(Harry Potter)

An Au where everyone is born having a soul bond connected to someone(more often then not a sibling but there are times it is to someone outside their family) who will be one of the most important people in your life(platonically).

Lily Evans and Severus Snape were born with a soul bond connecting them, Eileen expected something like this but didn't think her son would have a soul bond with a muggleborn.

Eileen knew that her son wouldn't be safe with her and Tobias so she went to the Evans and explained everything and requested that they raise Severus as their own to which the Evans parents accept as they could never forgive themselves for letting a child go back to one parent that will turn abusive once his magic is found out.

Lily and Severus grow up together and are very much like twins which annoys Petunia who is the one that has to get them out of trouble even if she is thankful for them as they helped her get rid of a boy that wouldn't accept a 'no' as an answer.

Anyways, imagine the time for them to go to Hogwarts arrives and the marauders meet them and the moment they say the first bad word about Severus, Lily would attack them as she would not allow anyone to badmouth her brother.

The marauders(mostly James and Sirius) keep trying to bully Severus especially as he still ends up in Slytherin and Lily in Gryffindor but neither of the Evans 'twins' allow it and when the friends Lily made ask her why she protects a 'evil' slytherin she turns to them with the fiercest glares and tells them that they may not respect the gift Lady magic gave her but she will not let anyone hurt her soul bonded which leads to a few realizations as everyone knows that someone's soul bonded are they everything and even when people fall in love and have kids, their soul bonded will still be one of their priorities.

This idea is a bit of a mess but it came to my mind after a fic I read.