It had been discovered weeks back that the measurements marked on the side of the pool were very much off from the actual depth of the water, but no one had wanted to bring it up with the staff of the school because they didn't want to lose access to the pool while it was remeasured and relabeled with accurate readings. That meant that, every time the students of Hope's Peak jumped into that water, they were throwing themselves into water that was easily half a meter deeper in some parts than it was in others, and always deeper than it said it was, but they were all strong enough of swimmers that they could handle the unmarked changes without there being too much of a problem.
The swimming pool was not for academic purposes, but rather for getting people to chill out and spend time together, so that they could ignore the stresses of school for a moment and get some peace and exercise. If they were to let the pool be closed, that would be stripped away from them for some unknown amount of time, and there was no one who was willing to put up with that for however long it took to set things right. Most of the students that came down to the pool were ladies looking to sport their cute swimsuits that they'd brought to school with them, but the occasional guy would be there to do some people-watching and enjoy the water for himself.
There was one exception to this "enjoying the pool for the recreation reasons" rule that everyone else seemed to believe in, and that was Byakuya Togami, who had never spent a minute down at the pool without being there just to chide others to get back to doing his school work for him. He felt that his time and energy could be better used in places that were kept in better condition than that pool was, and if he wanted to swim he made sure he got explicit permission to use the academic pool, which was cleaned and maintained far more regularly than the general use pool ever was.
One day, after being assured that people he'd rather not be around weren't going to be there, some of Byakuya's classmates convinced him to join them down at the pool, them swearing up and down that it wasn't going to be an open invite situation and that he wouldn't have to worry too much about certain people being there. He was still reluctant, but when Makoto promised him that if any of those faces were at the pool, he could be thrown in as punishment, that was enough to get him to at least agree to going down for a change.
It was true that when he got down to the pool, none of the people he wanted to avoid weren't there, but that was not to say that they weren't planning on showing up; in fact, the only people that were there when Byakuya showed up in his normal dress clothes were Makoto and Sayaka, who were both sitting in chairs on the far side of the water. "Hey, you made it after all!" Makoto called in greeting, waving Byakuya over to where they were. "Sorry that it's kind of bare in here right now, everyone chose not to show up or something."
"Almost wish I had made the same choice," Byakuya coldly replied, staring at his overly-accommodating classmate with steely eyes behind his glasses. "You aren't expecting me to actually get into this death trap of a swimming pool, are you?"
"It isn't that bad," Sayaka said, looking out at the water far too deep to be marked what it was. "You just have to make sure you stay where it's shallow, because once it starts getting deeper, you'll never know how deep it is."
"If it's shallow, I can touch the bottom. If I want to touch the bottom of the water I'm in, I'll just choose to visit a hot tub instead." Rolling his eyes, as if Sayaka's suggestion had been the single dumbest thing he'd had the misfortune of hearing, Byakuya considered just leaving right then before anything else happened, but he decided to humor the two and stick around for a little while. Drawing a chair up next to theirs, he sat down and listened to the two discuss who all they thought was going to show up now that their biggest guest was there. He wanted to drown them out, ignore what they were saying and how they were talking him up as some big draw for people to come see, but there was a piece of him that loved hearing his classmates acknowledge how important he was to the world.
Eventually, others started to trickle into the pool area, oftentimes not even saying hello to those who were already there before jumping into the water and sending splashes of water up to the watching crowd. Byakuya was mighty annoyed when Hina showed up and took it upon herself to kick water at him every time she swam past, but he didn't say anything because he knew his dagger-like glare would do the job for him. Sure enough, Hina eventually chose to swim on the other side of the pool, and as more people came in they joined her on that side to start.
Once the pool area was a lot fuller than Byakuya had expected and wished it would be, he got out of his chair and went to take his leave, no longer finding interest in what was going on. He intended on slipping out unnoticed, which would have been rather difficult given how many people were around him, but he was at least able to get past Makoto and Sayaka, as well as Kyoko who'd joined them on their other side, by choosing to go the long way around the pool. That put him right by the deepest, most unknown part of the pool, though, and if he were to slip or someone were to splash him, his chances of getting out unscathed and without slipping were rather low.
That was completely forgetting a third potential option, that being someone in the group seeing him over there and deciding to make a charge at him to knock him into the pool. He didn't even see it coming, in all honesty, with his focus being on getting out of the room and back up to his lofty dorm, but he heard it just before contact was made. Mondo was charging at him, rallied by the cheers of some of the ladies in the water, and when he got his hands on Byakuya he did nothing but push him forward, causing them both to fall into the depths of the water.
Byakuya could swim. He'd been doing all sorts of swimming since he was a little kid and his parents would drop him off at resorts under the supervision of nannies that let him do as he pleased. This, getting thrown into the pool like he'd been, was not swimming and was nowhere close to what swimming should have been, and even though the side said three meters deep he knew that he was going to have much further than that to reach the bottom. His arms felt heavy in the sleeves of his jacket, which was only weighing him down in the untreated water, and he struggled to get himself out of it to try rising back to the surface.
It didn't help matters much, as Byakuya felt like he was being pulled down into the abyss, unable to get back up to the surface even as he shed his expensive jacket and started working on his shoes. Soon, his lungs gave out on the air they were holding and he was gasping, taking in water that he simply couldn't breathe, and he was continuing to struggle to get back up to get some air. Up on the surface, Mondo had come up and was laughing about what he'd done, everyone else getting a good chuckle about it as well, until Sakura gently pointed out that Byakuya had been under for a while and that maybe he wasn't doing so well under the water.
His salvation came right as he'd accepted that he'd met his end, a hand grabbing onto one of his and pulling him upward. By the time he'd broken the surface and was back in the air, he'd taken in a fair amount of water and was teetering on the edge of consciousness, something that his mermaid in a one-piece swimsuit called out to everyone so that they could work on getting him the medical attention he clearly needed. He hadn't drowned, but he certainly came close to it there that day, and no number of apologies from Makoto going forward would ever make him go back into the pool that had cost him a jacket, his shoes, his dignity, and almost his life.
A/N: requests are still open, the card is on my tumblr!