It starts one night after a weird dream, when Ryouga wakes up and pads sleepily to the bathroom to get a drink of water and maybe pee before going back to sleep. He swishes some water into his mouth, and spits, and then he hears it:
and he looks down and sees a back molar sitting in the sink, with a little pinkish swirl of diluted blood rinsing down into the drain from its roots. Woozily, Ryouga thinks, (...what?...), and feels around his mouth with his tongue. There is a hole in his left bottom jaw where that molar had been, and as he pokes around with his tongue, he feels the next molar in line shift. That's weird, he thinks, and fishes around in there with his finger. That tooth comes free as well, and also the front incisor when his back knuckle bumps it as he pulls his hand back out of his mouth.
He looks at the three teeth in the sink, up to his confused expression in the mirror, down to the teeth again, back up, and then he smiles to check what he looks like. That is when it finally dawns that, oh my god, his teeth are missing, and he looks like a weird overgrown six-year-old with that front tooth gone.
Maybe he can tell everyone they fell out in a fight, he thinks, as he walks back to bed with a creeping sense of concern.
When Ryouga wakes up, there is a huge drool spot on his pillow, and six more teeth have come loose and fallen free inside his mouth while he slept. He hurries to the sink, where the three he'd lost last night still sit, and spits out the loose six - and as he does, another comes free with the suction that spitting required.
Ryouga looks up and opens his mouth. His teeth look like a carnival game.
"Rio..." he calls uncertainly. His sister walks in a few moments later, already dressed for school.
"Ryouuugaaaa, you really should get up mo--what did you do?" She runs over and pries her brother's lower jaw open like she's checking a horse. "You - You're! Did you - ? I - how?" she splutters.
Ryouga irritably backs out of her grasp. "I dthon' know!" he snaps. His mouth feels weird, half-empty and ...prickly. His gums hurt, too. "I wog up lass' nighth anth' -" Another tooth works loose and nearly drops into his windpipe; he chokes and spits it into his hand. The two of them stare at it.
"Let me see again," Rio orders, and takes Ryouga's chin again. He opens his mouth obediently, too worried about knocking more loose to struggle. "Hmm..." she says, gently turning his head to the side. "You haven't been eating any differently... what's this?" She takes her pointer finger and rubs it over one of the empty spaces. "You've got teeth growing back in."
"Ag's goo', rh'igh?" he gargles.
"I guess..." She pokes her finger in farther, and Ryouga tosses his head a little in annoyance. Her fingers taste like the salmon she ate for breakfast and it accidentally makes him drool a little. "You..." Rio's eyebrows are knitted with confusion. "Ryouga, there's more back there."
He spits her hand out of his mouth ("Eww!!") and feels his lower jaw with his tongue. Sure enough, he can feel multiple rows of tiny sharp bumps, like extra teeth are growing behind his teeth, and this is so weird because he'd already lost all his baby teeth years ago, so...??
"Wha'm' I gonna do?" he asks.
Rio glances into their teeth-filled sink with a grimace, and says, "Maybe... you should call in sick to school."
But that doesn't help much because, despite Ryouga's best efforts, every single one of his teeth manages to fall out over the course of the day, leaving his gums empty save for the tiny white ridges of teeth already beginning to grow back in. He feels weird, like a baby or an old person in a sick home. He's hungry. And to top it off, Yuuma comes to visit after school.
"Shaaaaaaaaaaaark," he yells out when he enters their small apartment, kicking his shoes off, "Shaaaaaaaaaark I heard you were sick, so we brought some okayu and I brought a blanket from home and - "
Ryouga glares at Rio, who archly crosses her arms and says, "Well, you needed someone to cheer you up." She crosses the room to where Ryouga sits on the futon with a blanket over his head. "Let me see - oh."
Ryouga can see Yuuma craning his neck across the room, and it just embarrasses him even more, so he snaps, "It's nothing, I just have some kind of teeth condition," except it comes out more like "I'ss nusssn', I j'ssus ha'son' kinna ssess' connisssshs'on'."
"Aww, sorry Shark," Yuuma says, and Astral even bothers to pop out of the Emperor's Key and ask if humans often break and will Shark be able to consume or eliminate energy if his teeth are gone, and in the meantime Ryouga tries to sip some of the rice porridge Yuuma brought, but Yuuma sees him, and insists on spoonfeeding him, and Ryouga doesn't get him out of the house until after dinnertime.
The next morning, Ryouga wakes up and realizes he can feel teeth in his mouth again, and he is willing to believe yesterday had all been a weird dream. That is, until he opens his mouth at the mirror and sees -
rows. Rows of perfect, triangular, razor-sharp teeth, teeth he can barely close his mouth over.
"Well, shhit," he says aloud. At least he only slurs his words a little bit now.
Yuuma is super excited at school. "Shark, Shark, do you know what this means? It means - you're like a real shark now! This is soooo cooooool! Can you bite through metal?"
"I'm about to bite you," Ryouga grumbles.
"Shark is kind of scary now..." Kotori mock-simpers, and she and Rio giggle a little.
"Don't compete with my darlings for the fish-nya," Cathy hisses, as if he were going to jump in the bay and begin life as a real sea predator. Ryouga rolls his eyes.
Yuuma's friend Shingetsu is laughing nervously. Well, more nervously than usual. "Haha... Shark-kun is so lucky! He'll probably grow pretty tall, soon!"
This comment was so weird that everyone in the group turns to look at him. Ryouga squints. What the? "Huuuh?" Yuuma says.
"I - You know, like, when your voice changes, and -?" Shingetsu is really flustered now, almost like he's panicking. Ryouga always knew he was sort of socially awkward, but this is a new record. "The - the ~change~?"
Rio rounds on him. "Are you talking about puberty?"
"Yeah!" Shingetsu brightens. "Yeah, that's the word!"
The whole group is dead silent.
"Shingetsu-kun, people don't grow shark teeth when they go through puberty," Kotori says very quietly.
Shingetsu is openly sweating now, and smiling with a sort of manic anxiety. "They... they don't." Everyone shakes their heads slowly. "...Ahaha, yeah, like, duh! I was just joking! You know, because the situation's so strange!" The end-of-lunch bell rings, and Shingetsu practically flees, yelling something about being late to class.
"Your friend'th really weird," Ryouga mutters.
About a week goes by and eventually Ryouga's new set of choppers just becomes a weird footnote to his existence. Some foods are harder to eat, some are easier to eat, and he has to enunciate very carefully now. One positive is that he's a lot more intimidating. And since his nickname was already Shark, no one felt the need to come up with any derogatory names, since they'd just sound stupid and superfluous.
And then one morning, Ryouga wakes up and his back is really itchy. He calls Rio in to look at it. "Ryouga, I don't know how to say this, but..."
His heart sinks. "Oh no. Oh my god."
"...You've got a big bug bite," she finishes, and laughs when he swipes at her.