2(Wind Breaker)

An Au where Endou Yamato and Sakura Haruka are siblings but are those siblings that would kill each other if given the opportunity but that would also would kill anyone who hurt the other.

So Sakura was still abandoned by his parents(it was during the time Endo went to Furin and so he was living in an apartment closer to Furin) but the moment Endo found out about it, he got his own parent in prison and inherited everything they had and owned before starting to look for Sakura while helping Chika take over Furin.

It was on the day of the supposed last fight between Chika and Umemiya when the detective Endou contacted found Sakura so Endo left to pick up his baby brother who then started to live with both Chika and Endou(and was constantly trying to pick a fight with Chika as he saw the way the red haired boy treated Endou but he stopped doing that after he and and Chika had a talk).

When it came time for Sakura to choose a school, he decided that he wanted to go to Furin like Endou did but asked to move out as he wanted to see how the school and Makochi were by his own and not be affected by Endou and Chika's reputation.

A bit unwillingly Endou accepted it and got a good apartment for Sakura(so no, Sakura doesn't live in the same apartment as he did in canon, it still is a pretty simple one at Sakura's request but much better then the one in canon).

How things go from here is up to the writer but I would like that when Noroshi vs Bofurin came to happen, it was mostly Endou and Chika trying to see if Furin was worthy of Sakura(it would also to be a scene were Sakura is trying to stop Endou from going to kill Togame and another of Chika beating up the KEEL members after the fight with Furin).