Posted originally on the Archive_of_Our_Own at https://archiveofourown.org/
works/13135653.
  Rating:
      Explicit
  Archive Warning:
      Choose_Not_To_Use_Archive_Warnings, Underage
  Category:
      M/M
  Fandom:
      モブサイコ100_|_Mob_Psycho_100
  Relationship:
      Kageyama_Ritsu/Kageyama_"Mob"_Shigeo/Reigen_Arataka
  Character:
      Kageyama_"Mob"_Shigeo, Reigen_Arataka, Kageyama_Ritsu
  Additional Tags:
      Alpha/Beta/Omega_Dynamics, Threesome_-_M/M/M, Sibling_Incest, Plot_What
      Plot/Porn_Without_Plot, Bath_Sex, sex_with_feelings, First_Time
  Collections:
      Yuletide_Madness_2017
  Stats:
      Published: 2017-12-26 Words: 3609
****** Chaperones ******
by 13lackbirds
Summary
     Mob unexpectedly goes into heat. Reigen and Ritsu are there to help.
Notes
     Happy Yuletide! :D I loved so many things from your letter, and I
     hope you have as much fun reading this as I did writing it for you.
     This is set some non-specific time fairly late in the manga.
Reigen is still getting dressed for work when there’s a knock on the door. Not
even a knock, really - it sounds more like someone trying to batter the door
down.
He opens the door, and is immediately shoved backwards by the translucent wall
of a psychic barrier. He’s grabbing for the salt in his pockets (even if it’s
ineffective against the supernatural, no human likes to get a handful of it in
the eyes) when he registers that the intruders are familiar.
The Kageyama brothers.
Ritsu is bristling with nerves, his aura a shifting array of color. He’s the
one keeping up the barrier, then, and one look at Mob makes it obvious why.
Reigen’s student looks like he’s about to pass out - he’s panting open-mouthed,
most of his weight hanging off his brother.
Reigen is just about to ask what the hell they’re doing when Ritsu drops the
barrier, and the smell hits him like a bus.
“Help,” they both say.
Fuck.
 
“Why did you bring him here?” Reigen reaches out to help support some of Mob’s
weight, ignoring how Ritsu tries to angle himself between them. Mob’s shivering
gets worse when Reigen touches him; Reigen determinedly disregards it.
"He brought me here." Reigen looks again, sees the way that Mob’s clinging
white-knuckled to Ritsu's gakuran, sees the way his hair is shifting over
itself. Yes, Mob can be hard to dissuade once he’s got an idea in his head.
The two of them deposit Mob on Reigen’s couch, and Ritsu continues. "We were
out - you were closer than our house," Ritsu says, the irritation in his voice
nearly palpable. Reigen eyes their school uniforms and doesn’t comment on how
obvious that lie is; he’ll talk to Mob about it later, give him a lecture on
truancy if he needs to.
“Master Reigen is a beta,” Mob mumbles. “It’s safe here.”
“We already got suppressant pills,” Ritsu says. “He’s just…”
His voice trails off, and he stares at Mob’s floating hair. Ahh. That explains
why Ritsu’s so tense. Mob’s powers coupled with first heat would be like
picking up two random chemicals and dumping them together - either nothing
remarkable would happen, or a lot of very dangerous things would happen very,
very quickly.
Nothing a little elbow grease can’t fix, Reigen hopes. “Nothing else for it,”
Reigen says, clapping his hands together. “He needs a cold shower.”
“Why?” Ritsu says.
"You know, it’s what you do when you need to...calm down.” This is tortuous,
really. Reigen can feel himself sweating. He tries to breathe through his
mouth, which is a mistake because then he can taste Mob’s pheromones on his
tongue. It doesn’t affect him the way it would an alpha, but it’s still
noticeable and - distracting. “If he’s taken suppressants it shouldn’t be that
much worse than normal teenage hormones. All he has to do is—” the image of Mob
touching himself springs into Reigen’s head and he nearly bites his tongue.
“...hose himself down, eat some greasy food."
To be honest, Reigen isn't sure if he’s remembering that last part right or if
he’s mixed things up with the cure for hangovers, but if nothing else it will
buy him time to think of something else to do. "Right now he's just kind of -
stewing in his own pheromones, so. He'll feel better if we get him washed off
and—what are you doing?"
Ritsu doesn't even look up from where he's unbuttoning Mob's gakuran. “He can’t
stand up,” he says, like Reigen is the stupidest person on the planet. Ritsu’s
face is red, his eyes focused but vaguely distant. Reigen can practically see
his hackles up, and alarm bells start going off in his head. Normally alphas
don't react to their siblings' heats, but— "We can't wash him in his clothes."
Yes, we absolutely can! Reigen bites back the thought at the last second,
barely keeping his cool. He needs to calm down; he’s the adult here. The one
Mob trusted enough to get help from. Still, it’s bad enough that he has to
babysit in the first place, he really, really, absolutely does not need to see
his student naked. Especially when Mob is noticeably hard and the sight of his
scrawny chest makes something come alive in Reigen’s stomach.
It must have something to do with Mob’s psychic powers. Yes, that’s definitely
it - he’s projecting his desire out into the air, the way a spirit can fill a
place with a menacing aura, and it’s strong enough that it’s rubbing off on
Reigen. Nothing at all to do with the odd excitement Reigen feels when he sees
Mob walk into the office after school, or the loneliness he can’t shake when
Mob isn’t there. Not his fault at all.
Reigen steels himself and goes to start the bath. He tunes out the sound of a
zipper, and Mob’s quiet sigh.
 
Reigen’s touched Mob countless times before, carted his unconscious body around
on his back even, but putting his hands on Mob’s nearly-naked body is a lot
more difficult to compartmentalize, even if he’s just helping Ritsu walk Mob to
the bathroom. This close Mob reeks of heat, thick in Reigen’s nose and on the
back of his tongue. His briefs are the only thing keeping him from being
completely exposed, and they barely hide anything.
Mob nearly wails as they shove him down into the cold water, convulsing in an
effort to twist himself out of the chill, and Reigen immediately knows that
they’ve made a horrible, horrible mistake, his mind nearly whiting out at the
sight of Mob’s stomach and thigh muscles twitching and his soaked underwear
clinging to him as he lifts himself out of the water. He hears Ritsu choke out
“brother,” and distantly registers the hungry expression that must be on his
own face when he meets Mob’s wide eyes, sees the start of an eerie glow at the
centers of his pupils.
Before any of them can say or do something colossally stupid, Reigen grabs the
shower head and sprays Mob in the face like he’s washing down a dog.
Mob squawks and sputters, falling back into the water with a splash that
drenches Reigen and Ritsu. The three of them scramble with each other, Reigen
and Ritsu on their knees and still half-slipping in the water on the floor, Mob
flailing like he’s attempting to avoid imminent murder. So much for Ritsu’s
insistence on not getting clothes wet. Reigen meets Ritsu’s eyes and they blink
at each other, and Reigen has to suppress a sudden, inappropriate urge to
laugh; it probably looks like they’re trying to drown Mob.
“Maybe it’d be more effective to fend him off with a broom handle,” he offers.
Ritsu sighs. “Shut up.”
Reigen turns the spray off again, warily. Mob lies mostly still at the bottom
of the tub, apparently resigned to his fate. Reigen watches in disbelief as
steam begins to coil off the surface of the supposedly-cold water. “Hey, stop
that,” he says. “You’re going to boil yourself.”
“Sorry, Master,” Mob pants, closing his eyes.
“We’re trying to help you, brother,” Ritsu says. Mob nods, his face crumpling,
and the windows start to rattle.
“Please, h-have sex with me,” Mob pleads, words polite and formal as always,
face red. Reigen and Ritsu make identical sounds, the breath whooshing out of
them as if Mob had kicked them in the stomach.
Reigen manages words first. “Mob,” he croaks, “that’s not a good idea.”
Mob arches and the room shakes, power surging, tiles cracking under Reigen’s
knees. There’s a high-pitched whine from somewhere, so loud Reigen can’t hear
his own voice telling Mob to calm down. Ritsu looks at him in a panic for a
moment before he leans forward, sprawling half over Reigen’s knees, and smashes
his mouth against Mob’s.
Normalcy returns immediately, the light its old fluorescent flicker, no sound
except for the wet noise of the brothers’ lips sliding together and Mob’s
quavering, drawn-out moan.
Reigen says, “Um.”
The two of them separate with a wet sound, spit trailing between their mouths,
and Mob starts to nearly hyperventilate. Ritsu sits back and yanks at the
collar of his gakuran so hard the top couple buttons fly off and clatter across
the tile. “Hey, wait-” Reigen says, trying to hold onto reason, but that’s all
he can manage before Ritsu is hauling himself into the tub, water overflowing
and soaking Reigen’s knees. Mob moans again and curls himself around his
brother, white skin stark against Ritsu’s soaked uniform. He hasn’t let go of
Reigen’s sleeve, and when Reigen tries to gently pry his hand off he tangles
their fingers together, squeezing hard enough to hurt.
Reigen leans his forehead against the side of the tub while he struggles to
hold onto the shreds of his composure. Mob is really such a sweet kid - he
wants to kiss, he wants to hold hands. Reigen’s dick twitches, more than half
hard, and the frantic whining and sloshing coming from the tub isn’t helping
that at all.
He lifts his head again, clearing his throat to tell them off.
Ritsu is holding Mob’s head out of the water with one hand while the other
moves back and forth inside Mob’s soaked underwear, not jerking him off but
pressing further back—
The words die in Reigen’s throat. He doesn’t moan, but the trade-off is that he
makes the most pathetic whimper-whine he’s ever heard out of a grown man. The
noise draws Mob’s attention, and their eyes meet just as Mob’s normally blank
face crumples in pleasure at the feeling of his brother’s fingers inside him.
Mob reaches for Reigen’s face, trying to drag him in. His eyes are wide and
glassy and he has his brother’s spit smeared across half his face. Ritsu turns
to look at Reigen with an expression that teeters between resentment and
desperation - he loves Mob more than he dislikes Reigen.
“Help me,” Ritsu snaps, yanking at Reigen’s shirt with shaking fingers, and
with how demanding the two of them are it’s almost too easy for Reigen to
abandon responsibility, wrap his arm around Mob’s skinny, naked back, and
encourage him to sit up so Reigen can climb in behind him.
Even though Ritsu asked for Reigen’s help, the two of them grapple for a moment
as they all try to crowd themselves together, fighting over Mob like street
dogs fighting over a bone, both of them starving for him. After a moment the
ridiculousness of it dawns on Reigen and he lets go. Ritsu’s competitive streak
is big enough for him to drown in, and Reigen is too mature to squabble with a
middle schooler.
Ritsu gently manhandles Mob back against Reigen’s chest, rubs soothingly at his
hips for a moment before he drags Mob’s underwear down and off. Saliva spurts
into Reigen’s mouth at the sight of him, flushed and hard against his soft
stomach. Reigen curls his own hands around Mob’s thighs,encouraging to spread
his legs as Ritsu fumbles his pants and underwear down. Mob is murmuring a
steady stream of please please please, and when Ritsu presses the head of his
cock against him he moans so loudly the hairs on the back of Reigen’s neck
stand up.
Ritsu takes a deep breath and rocks forward, pushing all the way inside in one
movement. They both nearly yell as he enters Mob, and Reigen sees Mob come,
just that easily, his head thrown back and his expression shocked, like he can
barely comprehend that his body can do this. Ritsu shoves his face into the
space where Mob’s neck meets his shoulder and makes a garbled noise, maybe
‘brother’ slurred with ‘please’ slurred with something unintelligible. He jerks
his hips, hard and rhythmless, jostling Mob against Reigen’s chest, against
Reigen’s aching cock.
It’s nearly too much for Reigen to stand. “Here,” he says hoarsely, fumbling
for Ritsu’s hips, “like this.” He’s half-expecting to get his hands bitten off
for his trouble, but Ritsu is too far gone now that he’s buried inside his
brother, drunk on Mob. He lets Reigen show him how to move, guide him to roll
his hips slower and with more purpose, angling in so he can hit that spot...
Mob loses it, his back arching, breath breaking off into a series of gulping
whines. His aura flares to life, blurry under the water, lighting Ritsu’s
scrunched-up face from beneath in a way that makes him look far more fragile
than usual. Mob mouths wetly along the side of his brother’s face, gasps his
name against his ear, and the mirror shatters as Ritsu comes with a low wail.
Mob shakes through it, his wet hair moving like he’s in the middle of a
tornado.
After a moment his head flops back, and his eyes blink sluggishly open. He
seems to take a moment to recognize Reigen, but when he does his attention
suddenly snaps into laser focus.
Reigen realizes what Mob’s about to do a second before Mob twists his neck and
kisses him. Or tries to kiss him. His open mouth presses over Reigen's, in any
case. It's sloppy, awkward both because of the position and the fact that Mob
clearly has no experience whatsoever beyond the frantic kisses he’d just
exchanged with Ritsu. It makes the knife-stab of arousal that much more potent
- yes, there's no denying that it's really Mob, out of his depth and subtle as
a block of cement as usual. He can feel Mob's gasping breaths and despite
himself, Reigen makes a ravenous noise.
Mob’s eager with his tongue, even more eager when Reigen licks into Mob’s
mouth. Reigen’s nerves feel scraped raw. Ritsu lifts his head and curls his
fingers into Mob’s hair, tilts Mob's head away from Reigen, and kisses him
again.
Reigen gapes at him. Possessive brat! He’s about to protest when Ritsu slips
out of Mob, and Reigen feels his expression change to one of spiteful glee. A
little too young to keep a knot yet, then. That’s just fine.
Reigen might not be an alpha, but he’s bigger than a thirteen-year-old.
Reigen shifts underneath them enough to fumble with his zipper, and Mob moans
when he realizes what he’s doing. Ritsu breaks the kiss and, to Reigen’s shock,
lifts his weight up so Reigen can pull his cock out. He’s so hard it hurts, and
the thought of what he’s about to do to Mob has his fingers twitching on his
shaft.
Reigen gets a hand between Mob’s legs, touches him where he's slick with
Ritsu's come, carefully eases his fingers inside. Mob is tight and fever-hot,
and he lolls limply against Reigen’s chest, content to just lie back and take
it now that he's getting what he wants.
Reigen lines himself up and can't suppress a groan as he begins to press
inside. Mob's worked up and worked open enough that there's no resistance, just
one slick, steady slide into choking heat. Mob shivers, his power surging, and
with the two of them connected like this the swell of energy goes through
Reigen as well, making his skin prickle and lifting his hair in a wave. Mob
feels so good, the clutching heat of him tight and perfect around Reigen’s
cock, needy, welcoming, accepting. His legs shake and his breath comes in
desperate little hiccups, like Reigen’s pushing the air out of him.
“Don’t pass out,” Reigen warns, voice as gravelly as if he’s just chain-smoked
a month’s supply of cigarettes.
Mob tries to speak, but it mostly comes out as breathy vowels. “If I do,” he
manages after a moment, something in his voice deadly serious even though he’s
falling apart on Reigen’s cock, serious in a way that makes Ritsu and Reigen
both shiver, “don’t stop.”
The position, frankly, sucks; with the weight of two people on top of him it's
hard to move. "Here," Reigen says, grabbing Ritsu's arm. "Put your arms under
his legs, help me hold him up." Ritsu happily complies, staring down between
Mob's thighs with a scarily intent kind of focus.
Reigen thinks about starting off slow, and makes it about thirty seconds before
his resolve melts under Mob's insistent whines like cotton candy under a
blowtorch. Ritsu bundles Mob’s thighs up against his shoulders, runs his hands
down between Mob’s legs, and Reigen feels him touch the place where Reigen
sinks into Mob, feels him begin to work his fingers inside too. Mob moans
frantically, voice cracking. Energy pours off him like heat off a fire. His
need is a physical weight in the air, heavy on Reigen’s skin, but what Reigen
and Ritsu are giving him isn’t quite enough—
Mob's head lolls back against Reigen's shoulder, his brows furrowed and mouth
open and slack. His voice is wrecked, but he still gasps and groans every time
Reigen hits that place inside him. The glow at the back of his eyes hasn't gone
away, and it gives his dazed, grateful expression a nearly angelic quality.
Ritsu pushes Mob’s drifting hair back off his forehead, his hand visibly
shaking, and Reigen knows with sudden, devastating certainty that they're both
going to think of this expression every time they jerk off for the rest of
their lives.
Mob fumbles for Reigen's hand again, laces their fingers together, and brings
it not to his dick but to the center of his chest. His heart thrums crazily
under their joined fingers, and something inside Reigen melts. With his other
hand Reigen grabs Ritsu's hip and and urges him forward so he can wrap his
fingers around them both, feel them slippery-wet and hard and straining against
his palm. Water sloshes over the edges of the tub as Reigen fucks up into his
student. His student. Mob, his student, the most important person in his
life...
Maybe he should have taught him better how to handle heat. Or maybe he’d taught
him exactly what he needed to teach him. After all, Reigen thinks a little
wildly, it’s better he’s here, with two people who really care about him,
instead of out there somewhere where anyone could—
Where he could—
Oh, yes.
He knows exactly what Mob needs.
Reigen presses his mouth to Mob’s cheek, speaks patiently into his ear. “Hey,”
he says, breathless, valiantly fending off his own orgasm while he tries to
keep up the pace and keep his voice calm and reassuring. “Mob. You did the
right thing, coming here. Your brother and I are here for you, you don’t have
to worry about losing control of yourself.”
Ritsu spills into Reigen’s hand with a long shudder, and Mob nods, frantic.
Reigen’s voice cracks, composure finally failing as he rushes out, “It’s okay
to let go a little, Mob—”
And then Reigen comes, harder than he ever has in his life, and Mob explodes.
It’s like holding onto a star trying to go supernova. The light that pours off
Mob is so bright it’s nearly tangible, there’s a roar like Reigen’s inside the
engine of a jet plane, and somewhere under that Mob is screaming - not a noise
of fear or pain, but of raw, giddy relief and happiness.
When the light dies down, they’re all shaking, and there's only an inch or two
of water left in the bottom of the tub - the rest of it is dripping off the
ceiling, condensed on the mirror and windows, or flooding the floor.
Ritsu flops forward onto Mob’s chest, his forehead resting on Reigen’s shoulder
opposite Mob’s head. Mob weakly wraps an arm around his brother and turns his
face to press a sloppy, shaky kiss against the first part of Reigen he can
reach. He moans one more time, tears gathered in the corners of his eyes, his
face full of gratitude. And then, finally, he swoons.
 
Afterwards, once the two of them manage to disentangle themselves from Mob’s
tentacular clutching enough to stand up, Ritsu holds Mob in his lap while
Reigen drains the tub and refills it so they can give Mob a proper bath.
The room is a mess, water flooding the floor, tiles cracked, every upright
thing knocked over. Reigen fully intends to have the brothers clean it up as
soon as they’ve all come down a bit more, but he grumbles about water damage
anyway. Mostly he just wants to have something to talk about, distract himself
from what he’s feeling. Ritsu doesn’t bother to acknowledge him. He’s too busy
looking at his brother, stroking his face and his sopping hair. Mob half-dozes
against Ritsu’s chest, looking exhausted and...well, well-fucked.
If they’re lucky, Reigen thinks, very carefully ignoring the twitch of regret
that accompanies the thought, Mob’s pills will kick in now that he’s over the
worst of the emotional onslaught. If they’re not, they’ll have a few hours
before he’s squirming again.
He’s glad he doesn’t have any clients scheduled today.
Reigen puts a hand on Mob’s head as well, on the opposite side from where Ritsu
is still touching him. He ruffles Mob’s hair a little, the way he always does.
Mob turns his face into Reigen’s palm, and for a moment Reigen thinks he’s
going to suck his fingers into his mouth, still thrumming with hunger for sex -
but he doesn’t, just nuzzles. He wants to be petted, cuddled. Appreciated.
Reigen looks at Mob, and then at Ritsu. On an impulse he ruffles Ritsu's hair
too, and is rewarded with an expression of such profound disgust he can't help
but laugh.
Maybe things won’t be so different from now on after all.
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