The stuff about the amygdala that I mention is all true.

Kurisu takes a long time to fall asleep that night. Her thoughts are occupied by Okabe: why on earth the younger version of him is so shy and quiet, and brainstorming a way to fix the situation. She still remembers how to build the time leap machine, and asking Daru to hack SERN again is an easy task. But what would the time leap machine accomplish? Its range isn't far enough to send Okabe back in time ten years, and even if it could, there's no way to return older Okabe to the present. Not to mention, Kurisu remembers sadly, Okabe wouldn't want her to build it. He had been so angry when she built it before. No, not angry—scared.

The version of Okabe she'd met when she had traveled back in time had been quiet as well, and she wonders if the loud, obnoxious personality she's accustomed to is just part of his mad scientist persona. Another possibility occurs to her. Okabe had adopted his mad scientist persona as a way to assure Mayuri that she was still needed. The ostentatious loudness could be meant to reassure Mayuri as well, to remind her that even with her grandmother gone, she still had people that cared about her. It would certainly explain the drastic differences between his older self and his younger self.

Fortunately, whatever had happened to Okabe had occurred on a Friday afternoon, so they were all able to stay at the lab and attempt to find a solution. They fall into a routine; Mayuri entertains Okabe and keeps him occupied with easy conversation and TV, while Kurisu and Daru brainstorm, helping out occasionally, and eavesdrop on their conversations. Kurisu has decided that Mayuri must be some kind of miracle worker, because he hasn't asked to leave the lab or to see his parents once.

The somewhat comfortable routine they've fallen into is disrupted Sunday evening. Daru announces that he won't be able to return to the lab until the next afternoon, because he has to go to class. This isn't too much of a problem, and anyway, Daru can help by telling Okabe's professors that he's sick, since Okabe obviously won't be attending his classes.

She's forgotten about Mayuri, though. At first, Mayuri is determined to stay with her friend, but Kurisu manages to convince her to go to school, reminding her that she can come over to the lab as soon as classes are over. "Besides," Kurisu continues. "I don't have any lectures tomorrow, so I can stay here with Okabe."

Mayuri looks dubious at her suggestion, but eventually is convinced enough to start heading home. Kurisu can't blame her, she's trying to sound more confident than she actually is. She's not very good with children on a good day, let alone with a ten-year-old version of one of her friends. She's determined to help though, and that has to count for something.

Monday morning is awkward. Kurisu manages to keep Okabe occupied with the TV, but the silence in the room is heavy, and she doesn't know what to do. Okabe finally breaks the silence when she's in the middle of going over her notes for the lecture she's giving on Wednesday. "What's that?" he asks, pointing to a structure on one of her diagrams of the brain. Apparently he's been reading over her shoulder.

Kurisu is surprised by his interest. "That's the amygdala," she explains, and his eyes light up with interest. "It's involved in strong emotions, especially fear." He nods, and they quickly fall into a routine; he asks questions, she answers and explains. It's good practice for when she actually gives the lecture, and it's keeping him occupied.

She can't help but notice how, at ten, he's very perceptive and learns quickly, even though the topics she's discussing with him are confusing for even the top college students in her classes. She begins to wonder if there's some reality to his claims that he's a genius; if he's this smart at ten, then who knows how smart he could be in ten years.

The day goes by quickly once Okabe expresses an interest in her favorite subject, and when Mayuri comes running in after school, she finds them sitting comfortably together on the couch, still going over the lecture notes, Okabe peppering Kurisu with endless questions.

They finally break up the discussion when Daru returns, so they can decide on a plan of action for the rest of the week. Kurisu has just turned around when Okabe starts suddenly, and gasps, just like he did before. He starts gazing around at the lab again, this time in relief.

"Okarin?" Mayuri presses him. "Something wrong?"

There's a moment of silence, then Okabe responds, "Nothing's wrong, sweetheart. In fact, I'd say that everything is as it should be."

"You're back!" Mayuri squeals, and proceeds to tackle him in a hug. Daru and Kurisu both sag with relief.

"I hope I wasn't too much trouble?" Okabe asks, returning Mayuri's embrace.

So he remembers what happened. Daru goes to make a sarcastic comment, but Kurisu elbows him in the ribs and responds, "No trouble at all. We had it covered." Mayuri is speaking rapidly, telling him everything that happened during the mind switch. Kurisu smiles, lost in thought. This incident has given her a lot to think about. Regardless of the consequences of Okabe's swap, she's glad to have him back.

The End?

Probably, although I may write an epilogue at some point.