Second fic for a fic exchange between myself and multishippingexpert. Prompt for this one was "collision".

Being greeted by Nagisa-kun, Rei could conclude after several months of knowing the boy, was inevitably and incontrovertibly akin to what he imagined entering into collision with the core of an atom was like.

Nagisa-kun was all positive energy rushing towards you, hoping to share himself, and half the time you didn't even see him coming. The collision itself was even more… intense.

Rei would find himself exiting the train at the school's station, nose in a book, nonetheless being mindful of where he was going. Running into people was not beautiful – for either party. Suddenly, a certain Hazuki Nagisa – who had been on the same train as him but not managed to be in the same car (due to their different stops) – would plant his face firmly into Rei's shoulder, arms coming up to grab at him and make him lose focus on his physics book. Eventually, he would calm down, but only once Rei had ceased his protests and properly greeted the now pouting boy.

Thus, the collision itself left him relatively unharmed. But, like a meeting with the core of an atom was want to do, it also left him with an abundance of positive energy that he was simply not used to having, and which he dealt with by squirming. Not always outwardly, but his brain would race faster and he would find his hand rising to his face to adjust his glasses more often than was needed.

In class, his brain would squirm the most, churning with thoughts of physics and lessons and swimming and how Nagisa was two rows behind him and blissfully unaware of the consequences of his energy giving. He was able to complete his math problems even faster than usual, but that only left more time for his brain to cycle with thoughts of that morning's embrace. He could have sworn Nagisa brushed his hand down his back on purpose, reaching dangerously low, as he pulled away. Rei reached up and pushed his glasses back up his nose, the breadth of his hand stretched across his face hiding his blush from his classmates.

When not in class, he tended to squirm both physically and mentally. He just wanted to go eat lunch, but Nagisa-kun had been accosted by several girls from another class who were shyly offering him sweets they had brought from home. Rei's foot tapped a steady but slow beat, and his hand lingered on his glasses for a few seconds while his brain flatly rejected the girls' presence. Rei suspected that if he were to invent the proper kind of detector, he would be able to garner physical proof of their inner squeals and excitement at being close to Nagisa, they were being so obvious about it.

The same kind of squirming, though once again more mental than physical, made itself known during lunch itself. The girls had departed and Nagisa-kun had skipped and cheered his way to the roof to meet Makoto-senpai and Haruka-senpai. Rei had taken a seat, greeting the older boys simply – the squirming had begun once Nagisa-kun felt the need to honour both of their senpai with one of his atomic collision greetings.

Swimming practice was fortunately a field of study that required energy, and it allowed Rei to work off any lingering excess that Nagisa-kun's embrace had caused.

Of course, the boy was also on the train home with him, so he was not yet free of the energy he could still feel emanating from the seat beside him, even as he fell asleep on Rei's shoulder. Rei always had to wake him up at his stop, and prod him to get off in time. Often, Nagisa-kun would grumble, adjust his head and mumble that he was staying over at Rei-chan's tonight. And of course once they arrived at Rei's house, Nagisa-kun would be just well rested enough to attempt to distract him from his homework for the rest of the evening.

Today however, he had heeded Rei's attempts to wake him up and stumbled off towards his own dwelling. Rei was thankful, as he felt that perhaps there was more to his squirming than a mere excess of energy – even if Nagisa-kun did have an abundance of it – and he wished to do some soul-searching in private.

Rei was not one to ignore his feelings or misunderstand them for very long – but this merely led to a semi-permanent blush on his face for days after his nighttime emotions-analysis.

Squirming, in correlation to Nagisa-kun's presence, in correlation to the effect Nagisa-kun's presence had on him, and others, in correlation to the fact that Nagisa was not in fact the core of an atom but rather much more than that – well, there really was only one conclusion. Amakata-sensei had spouted enough romantic sayings during swim practice for Rei to understand what was going on in his own mind.

Though the conclusion brought a certain sense of peace – Rei was a scientist after all, he enjoyed knowing over not. Not knowing was not beautiful – it did not stop him squirming, in fact it just added to it. And though he now knew his own mind, questions still popped up regularly.

Did Nagisa smile at everybody like that?

What was the force that Nagisa-kun had to use in order to launch himself across that particular distance onto Rei?

Why was it approximately 11.5 times worse when Nagisa-kun laughed at him after his violent, embarrassing and completely not beautiful dive-awakening in class, than it was when anybody else laughed at him?

Did Nagisa-kun really have to choose that speedo for today's practice? Surely a full-body suit would be faster? And it was getting cold, perhaps he should offer Nagisa-kun some pants and a sweater. Perhaps his sweater, if Nagisa-kun hadn't brought one. He did have a spare.

Directly after his realization, Rei had decided to test his hypothesis further, to confirm his theories, even though he suspected the constantly cycling questions were indicative enough.

He worked up a schedule, finding ways to avoid Nagisa-kun thoroughly but not suspiciously for three days, then allowing himself to spend slightly more time with the boy for three days. The first step proved difficult, the second easy; all he had to do was allow Nagisa-kun to sleep on his shoulder all the way to Rei's own stop on the train, and then allow the boy to stay the night again.

His results were nothing short of conclusive, but he needed to repeat the process. No good experiment contains only one set of values/observations. Ideally the process should be repeated until an average of ten or more sets of values can be determined. Rei decided that this would be a bit much, and settled for an even four.

However, his plans were dashed completely on the third day of his second attempt at avoiding Nagisa-kun for a time.

When he attempted to shoo the boy off his shoulder and off the train at his stop, it was to find Nagisa-kun rather surprisingly awake, glaring fiercely with a sudden death grip on his arm. The blonde had said, enunciating very clearly through his pout, that he was staying over at Rei-chan's tonight.

Rei was shocked enough at this development that he offered no complaint.

It was only once they had reached his home and Nagisa had made a beeline for Rei's bedroom, planting himself down in the middle of the floor, the pout/glare combination returning to his face, that Rei slowly closed the door and asked what the matter was.

Nagisa pointed firmly at the floor in front of him. Rei sat. And waited. Nagisa was rarely silent for long. He would tell Rei soon enough.

Nagisa looked at Rei. His glare diminished, though the pout stayed. He squirmed a bit. His pout deepened. He looked to the side. Rei almost wanted to take notes. He'd never seen Nagisa-kun like this. It concerned him as much as it made him curious.

Finally, brow furrowed, he decided to ask. "Nagisa-ku – "

"I LIKE YOU, REI-CHAN!... A LOT! THE MOST! – I know Rei-chan has been busy but I like to spend time with you so please make time for me and I LIKE YOU VERY MUCH!"

Magenta eyes were wide. Rei could guarantee his own were as well. Nagisa must be serious, for him to be behaving so nervously, so little like his usual mischievous self. The thought sent a swoop of joy through his brain, even though he was still relatively frozen in shock. However, though he was surprised, he was sure that if he were able to measure bravery, he would have seen that it had taken a lot of it for Nagisa-kun to say such things.

It was only fair that he honour that with some kind of equivalent exchange (a concept from a favourite anime of his).

And so, Rei, abandoning thoughts of notes and experiments, rocked forward on his heels and awkwardly planted his mouth on Nagisa's.

The END

Right, so nothing and nobody can convince me that Fullmetal Alchemist would not be Rei's favourite anime.

So, I don't know if you guys noticed, but when Rei is thinking about Nagisa as more a scientific anomaly, as his test subject, he refers to him as "Nagisa-kun" which is more formal. When he isn't thinking that way and is instead overwhelmed by teenage feelings of embarrassment and having a crush and you know, hormones, he refers to him as just "Nagisa".

Also, I honestly feel that sometimes, Nagisa just isn't as mischievous and in control as he seems. I think when it comes to dealing with crushes, he would be just like any other teenage boy. Nervous and with a tendency to blurt things.