Kageyama and Ennoshita would be quite traditional about it. When they got a moment alone with them in an intimate setting, they would take their partner’s hands in their and ask them with the utmost sincerity, if they would like to go to prom with them.
That dork Bokuto would go all out with his promposal. He’d show up at school with a bouquet of roses, and ask them in front of everyone - much to his partner’s dismay.
Oikawa would perhaps be just as showy about it, which also helped to ward off any fangirls. He would turn up at class with their favorite flowers, proclaiming that they would be his prom date.
Tsukishima would spend some time fussing over how he should ask them. In the end, he would bring it up quite casually, when they were cuddling on the sofa or something. He would remain cool on the outside, but his heart was nearly beating out of his chest in anticipation.
Hinata and Nishinoya would be the type to ask their partner to prom after winning a volleyball match. In the heat of the moment, they shouted up to where their partner was sitting, asking them to go to prom with them - in front of a gymnasium full of people.
As for how Sugawara would go about asking his partner to prom, I think that he would bake them cute little cupcakes - and across all of the icing would say ”Will you go to prom with me?”.
Asahi, being too embarrassed to ask them to their face, would leave them a a stuffed bear and a note in their locker, saying ”I couldn’t bear it if you went to prom without me”
what a fuckign dorkKenma would ask his partner in a similar way, perhaps leaving them a little letter in their locker or something, with a little poem written on it.
Tanaka, not to be out-shined by Bokuto or Oikawa, would write ”Prom?” on 100 ping pong balls, and stuff them all inside his partner’s locker. As soon as they opened it, the message would be pretty clear.
Kuroo would ask his partner when they were having a night in, just sitting watching movies. He would order pizza for them, but specifically requests the delivery person to write a message on the inside of the box. When his partner opened the pizza, it said; ”Will you go to prom with me, or is this too cheesy?”
Sawamura and Yamaguchi would take their partner out for lunch, or for dinner when they were going to ask them. Yamaguchi would ask them whilst they were out, organizing to have their dessert delivered with a little message on the plate saying, ”Prom?” Sawamura would walk them home, and once outside their house, he would pull them closer to him and ask them ”Will you go to prom with me?”.