SO i was going through my list of prompts from tumblr and this one stuck out and i was like OHMYGOD so i wrote it even though its not quite make-believe but whatever

(i may or may not be obsessed with this au)
((and i may or may not be planning out another that uses my favorite au ever which is trans!hinata))

Shouyou and Tobio frequently have play dates. Hinata would often ask to see the other boy by saying he wanted to hang out with his "best friend", and when Tobio spent the night, they had to sleep next to each other, whether together on the bed or on the floor. They were nearly inseparable despite their regular fights. However, when Tobio suddenly declared that he was going to marry Hinata, Koushi was a little put back.

"Hinata is going to be my bride," he said, looking as determined as a four year old possibly could be. "He's gonna wear a big dress and cook me food-"

"Wait!" Shouyou cried frantically. "I'm gonna marry daddy, not Tobio." 'Daddy' was Koushi. He thought it was incredibly adorable the first time Shouyou said it, even if Daichi had teased him about it later. He could remember saying the same thing to his own mother when he was young. Of course, Shouyou didn't actually know what marriage entailed; they had explained marriage as when you have a special someone, and you want to spend the rest of your life with them. Obviously, as a small child, Shouyou would immediately think of his father.

"You can't marry your dad!" Tobio retorted, frowning.

"Yeah I can." Shouyou replied stubbornly. You could almost watch the anger bubble up in Tobio then, and, in an act of pure, uncontrolled rage, the dark haired boy went up and pinched him on the arm. Shouyou instantly started crying.

Daichi came into the living room as Koushi picked Shouyou up, cradling the bawling boy against his chest.

"What happened?" Daichi asked, and Koushi, lightly rocking his son, explained. By then, Tobio had calmed down and looked on the verge of tears himself.

Koushi knelt down in front of him and gave him a small smile. "Tobio, you have to be nice to Shouyou if you're going to marry him. That's how being married works, okay?"

Tobio sniffed and nodded.

Shouyou, however, was not so easily pleased.

"No! I'm not gonna marry him! I'm gonna marry daddy!" he held on tighter to his father's neck, and Koushi sighed.

Daichi came to his rescue. "You're both too young to get married." he said, and they looked at him incredulously.

"How old do we have to be?" Shouyou asked.

"50." Daichi didn't so much as blink, and Koushi had to hold back his laughter as kids gaped.

"That's really old!" Tobio exclaimed.

"So you don't have to worry about it for a long time. Now, be nice and play or I'm calling Iwaizumi to pick you up."

"Okay..."

It was rather peaceful after that. Tobio and Shouyou played without injury, leaving the marriage conversation behind them. It was when Oikawa and Iwaizumi came to grab Tobio
that it came up again.

"Shou, will you marry me?" he tried again, frowning at Shouyou grumpily.

"...Maybe... But you have to be really nice to me! No more pinching!" Shouyou said, and Tobio gave a nod. "And you have to be the bride!"

Tobio gave a look of revulsion. "No way! You're the bride!"

"Nope!"

Oikawa and Iwaizumi hadn't heard of new development in their child's relationship, and were surprised to say the least.

"It's time to go, Tobio." Koushi intervened, patting the boy on his head. Tobio gave one last look at Shouyou, stuck out his tongue at him, and left with his parents.

Shouyou stuck his tongue out back just a little too late, and ended up doing it to the door. He turned to Koushi.

"Do I have to be the bride?" he asked solemnly.

"Of course not, Shouyou." Koushi responded. "Neither Dad or I were brides when we got married."

"Yeah?" You could never be too sure of something.

"Yep." ...Or maybe you could, since Shouyou simply grinned and ran back into the living room, yelling about a TV show.

"Kids are such a hand full." Daichi commented, coming up beside Koushi. "I don't think I was this much trouble when I was their age."

"I don't know, I think I wanted to marry my mom back then. Never my best friend though. That came later." he smiled.

"You never know, maybe they really will end up together." they both laughed softly, then followed their son.

((They find out Daichi is right when Shouyou is fifteen when Koushi accidentally walks in on them kissing. They're both so embarrassed that he manages to keep it in long enough to apologize and leave, but as soon as he's gone, he cracks up. The next thing he does it call Daichi at work to tell him he was right.))