This is inspired by a headcanon from the daily-okakuri blog on tumblr. Mayuri is about 8, and Okabe is around 10.
"Please?" Mayuri begs for what seems like the hundredth time since she handed Okabe the flyer. "I don't want to go by myself!"
"No way!" Okabe responds, shaking his head. Mayuri makes a pleading face at him; her eyes are wide and sad. Unfortunately for him, she's slowly worn down his resistance over the past hour. Her giving him the puppy-dog eyes finally gets him to agree. Grudgingly, he sighs and surrenders. "Fine, I'll go, but I'm not wearing those—ridiculous outfits!"
Mayuri squeals with joy and tackles him in a hug. "Thank you, Okarin! It'll be fun, I promise!"
She skips out of the room to tell her mom the good news. Okabe lays on the floor of the playroom, wondering what he just agreed to.
Dance Lessons. He was going to do dance lessons with Mayuri.
Okabe had been certain that this was going to be terrible. After the first lesson, he realizes that this is going to be even worse than he thought. Upon arriving back at Mayuri's house, he flops to the floor of her playroom with a huge sigh, determined not to move until he sinks through the floor into the depths of the earth.
"Oh come on, Okarin, it wasn't that bad," Mayuri tries to reassure him, nudging him with her foot. He gives a disbelieving snort. "Okay, maybe it was," she admits gently, twirling her fingers through her hair like she always does when she's thinking about something. "But still, I'm sure we can find a way to make this better." She gasps, and claps her hands. "Oh! Mayushi has an idea!" She offers him her arm.
"I'm not getting up," he responds, looking at her dubiously. "Ever."
"Come on, Okarin!" Mayuri insists, tugging at his arm. "You're going to get better at this the same way you get better at anything! I'll practice with you!" She offers her arm again, and this time Okabe gives another dramatic sigh and pushes himself off the floor to stand next to her.
"Okay," he says tentatively. "Where do we start?"
She lights up immediately at this. Mayuri, of course, had taken easily to dance, her natural grace and enthusiasm serving her well. "Mayushi will teach you! First, you put your right hand here, and your left hand here, and you put your feet apart like this, and . . ."
Mayuri's dance lessons pay off, and soon she and Okabe are the stars of their class, until Mayuri gets bored and quits, which allows Okabe to stop as well. It's not something he brags about or mentions to their other friends, once they finally have some. But Mayuri keeps several photos of them dancing, and he keeps a couple as well, even tucking one away in the lab where no one will find it.
Much later, when they practice for the first dance at their wedding, Kurisu will shake her head in disbelief and ask how he got so good at dancing. He smiles mysteriously at her and laughs. "Practice, my dear assistant."
