This is pure self-indulgence, based on something that I wanted to happen in the anime. Set post-anime. Constructive criticism is welcomed!
The day is hot, and the windows of the lab are thrown open to catch the breeze, despite Okabe's protests that they might be overheard by the organization. The heat has made everyone more irritable than usual, with the exception of Mayuri, who is still ecstatic about having a new female friend.
Before she speaks, Kurisu glances around the lab. Okabe and Mayuri are seated next to each other on the couch with their heads together, quietly discussing something. Daru is at his computer, working on something either illegal or disgusting, perhaps both. Kurisu has been standing awkwardly next to the couch, still not quite sure where she fits in.
She's incredibly grateful to Okabe for saving her life, but no matter how strongly she's drawn to him, she still feels like an outcast in his friend group. She has an impression that she knows these people well, but she has no concrete memories of being with them. It makes her nervous, and, as she's recently discovered, Kurisu lacks people skills. This, combined with her limited experience with having friends, means she is constantly ill at ease when they all gather at the lab.
Okabe asks her something, and as quickly as they've started talking, they're arguing and he's teasing her. Normally, the most comfortable Kurisu feels around him is when he's teasing her, but today, she's hot and impatient and nervous, and takes it badly. His refusal to use her given name, instead calling her once again that stupid nickname, "assistant," is her undoing.
"For the last time, I am not your assistant!" she snaps loudly. It's almost a shout, and everyone snaps their gaze to her. The relative tranquility of the lab is shattered, and Kurisu feels nerves bubble up in her stomach. They're the impetus for her next words. "You are impossible!" she yells, suddenly furious. She turns to Mayuri. "Why do you even hang out with him?" she asks recklessly.
As soon as the words are out of her mouth, Kurisu wants to take them back. One of her worst qualities is that she tends to be blunt, which serves her well in the line of scientific inquiry, but tends to sabotage her in her personal relationships. This time, she fears she might have pushed too far.
On the couch, Okabe slumps, already aware of where this conversation is going to go. He prepares himself for Mayuri's answer, and for Kurisu to react predictably and assume that he's a creep. It's exhausting sometimes, he thinks to himself, being the only one that remembers things from the different timelines.
But really, this is his own fault. After all, he's never told Mayuri how much she means to him; he'd always assumed that she already knew. But recent events have convinced him otherwise, and made him realize how much he needs to fix things with her. Mayuri still thinks she's just a hostage, when she's the most important person in his life.
Mayuri surprises both of them when she shakes her head, smiling slightly. "You know, for a smart person, you sure ask a lot of silly questions, Kurisu," she admonishes gently. "I stay with Okarin because he's my best friend."
Okabe's head snaps up—that was not what he was expecting. He was expecting a long, awkward, tedious conversation, not a simple confirmation from Mayuri. He resolves to buy her a thousand metal oopas. And cosplay fabric. And whatever else her heart desires.
"Okarin's always been there for me, and I'm always there for him. That's what friends do for each other," she explains simply. "We accept each other." She clasps Okabe's hand in her own, grinning brightly. He's too shocked to say anything, and instead just returns the gesture, gripping her hand in return.
"You guys want to order pizza for dinner?" Daru asks obliviously, breaking the moment. Kurisu immediately answers, grateful for the change in subject. Soon they're bickering over toppings, with Mayuri occasionally adding her input. Okabe is lost in thought, and doesn't contribute until Mayuri nudges him, effectively breaking him out of his stupor. Their hands are still clasped together.
That night, he and Mayuri are the last ones left at the lab. He's been lost in thought all day, trying to puzzle out the right thing to tell Mayuri. His thoughts are interrupted by Mayuri.
"Hey, Okarin? Are you in there?" She tips her head at him, concerned. "Do you remember the sleepovers we used to have? We used to stay up late and watch the stars." She smiles to herself, lost in memories.
Okabe chuckles. "Yeah, I remember that you always used to fall asleep on the roof when we were stargazing, and I'd have to carry you downstairs." They both laugh for a second, and then Okabe sobers. "Mayuri?" He swallows, gathering his courage.
"Okabe?" She looks worried, her questioning eyes focused on his face.
He wraps her in a tight hug, burying his face in her hair. "You know—" he breaks off nervously, then continues. "You know that no matter what happens, you are important to me. You are the most important person in my life, and I need you to know that."
Mayuri is quiet for a moment, then he feels he shift so that she can embrace him back. "Thank you, Okabe," she murmurs, so quietly it's almost inaudible. Okabe breathes a sigh of relief, clutching her tighter. For the first time in a while, he feels that their relationship is strong, the bond between them renewed.
