3(Haikyuu)

So this idea came from recently reading a few soulmate au about IwaOiKage, KuniKinKage and IwaOiKinKuniKage.

Something that they share is that at some point at least one of them rejects Kageyama due to the King of the Court thing or jealousy but this troupe gets a bit tiring.

So what if, Oikawa realized Kageyama was also his and Iwaizumi's soulmate when he almost hit him and choose to take a step back and try to thin logically? Instead of rejecting Kageyama and dragging Iwaizumi to do the same, he took the time to think and realize his thoughts did not make sense so he wrote a letter for Kageyama were he apologized for his actions and asked him to not directly interact with him for some time as Oikawa wished to not hurt him or almost hurt him again and had Iwaizumi give it to Kageyama? Oikawa goes to therapy and the only contact he has with Kageyama during this time is exchanging texts with him while he allows Iwaizumi to freely interact with Kageyama as it is Oikaw's problem who stops him from treating Kageyama right and Iwaizumi has his own free will

But Oikawa never really tells Kageyama and Iwaizumi about being soulmates(not because he did not want but because he forgot about as he considered his behaviour much more worrying then informing them of that).

So when KinKuniKage find out that they are soulmates, none of them think they have two more and become very close as they supposedly must have been in canon or even more.

But as Kageyama starts to suddenly change in their second year, KinKuni does not force Kageyama to talk to them about what is worrying him but they show they are always there until he opens up about his sister being in Tokyo and his grandpa being sick so Kageyama is alone at home and is the only person who visits his grandpa in the hospital.

KinKuni decide to ask their parents to stay with Kageyama(which while reluctant, they accept after hearing what was going on as long as the trio stay sometimes at Kin and Kuni's family houses) and go with him to the hospital so even when Kazuyo dies during Kageyama's third year, he does not become a tyrant(he goes somewhat mute when it comes to others but no tyrant) and has Kunimi and Kindaichi to help him grieve.

Iwaizumi and Oikaw when they hear about Kazuyo's death from KinKuni, they also offer comfort which is also a good time as Oikawa's therapist allowed him to slowly start interacting with Kageyama in person.

When it comes to choosing a school, Kageyama decides to not go to Seijoh as while he would love to have more time with Oikawa and Iwaizumi, he wanted to extende his wings so he tried to join Shiratorizawa which wasn't successful so he ended up joining Karasuno with KinKuni following him(just because I'm curious on how things would go if KinKuni also were part of Karasuno).

It was on the summer before their first year, that Oikawa revealed about Kageyama also being his and Iwaizumi's soulmate which lead to the five of them discovering they were some of the rare people with a five people poly bond.

How this all would affect anything else in canon is up to the writer as it is others ships and what type of soulmate au this is.