IF ONLY ღ r. matsuyama x fem! reader
༉‧ .| synopsis: You were the only person who ever truly believed in his theories. Until an unnamed tragedy changes everything, leaving Ryuji to chase answers in the space between worlds.
˖ ִ𐙚 | warning(s)—mentions of death, heavy angst, smut— dick riding, tummy bulging, Ryuji is mentally unstable (mentions of suicidal attempt)
⋆.˚ | author's note: Hi, my angels! Uni has been mopping the floor with me. I'm so sorry for my long hiatus. Im currently free from the shackles (winter break), For those of you who remember me, hey!! I recently watched AIB S3, and this very complex and morally grey man has been stampeding through my mind nonstop, so here ya'll go!
“Do you believe in alternate universes?” You murmured against his lips, your breath warm and sweet with strawberry sake. “It’s not impossible. Stephen Hawking practically laid the groundwork for it." His hand slid down your waist, fingers tightening at your hips, a rare smile softening the usually unreadable line of his mouth.
“Well…” you drawled, brushing a loose strand of hair from his face. “I read your research—about that place you described… a realm suspended between life and death.” Your voice brushed against his mouth like a whisper, soft and assured. “It sounds metaphysical, sure. But also… strangely possible.”
“Possibility isn’t enough in academia. I need evidence. I need… something real.” He exhales, his thumb gently rubbing circles into your sides. Every academic he had turned to rejected his research, claiming it was philosophical rather than scientific, even the head of the psycho psychology department denied the existence of such a world, such a product of one's deepest subconscious mind. They refused to read it and refused to indulge his study. All but you. You drew in a steady breath, gently removing his hands from your hips, intertwining your fingers with his own, promising him, “Then we’ll find a way to make it real. Maybe not tomorrow, and maybe not in the way traditional research expects—but the path is there." You paused, your lips pressing against the corner of his mouth. "You’re exploring something most people are too afraid to even question. That alone tells me you’re on to something.” The tense crease between his brows eased, his tension slowly melting away. "You really think so?"
"I really do..." Your lips gently press to his knuckles before flashing him a small, hopeful smile. "Whatever direction this takes, you won't be facing this alone. The critiques, the questioning. I'll be here through it all, and you'll prove them wrong; we'll find a way."
His lips press against your forehead, letting his eyes fall shut as he stills for a silent beat before meeting your gaze.
"Okay." You meet his gaze with a tender smile before gently letting your hand fall from his cheek, walking over to your desk, and reaching for the last of your research papers, carefully organizing them into a folder overflowing with your findings and sketches.
Your Ph.D. research primarily focused on frontotemporal gamma activity, which is closely related to lucidity, and how it affects children. Many of your mentors praised your work, claiming you would one day redefine neural research on sleep patterns and brain waves. The praise was nice; it was always pleasant to know that people appreciated your work. Ryuji, on the other hand, faced much harsher criticism for the specularity of his work. Most claimed it was more philosophical than scientific and could not be proven with real data and experiments. He was determined to prove them wrong, to deliver groundbreaking research to the university and the rest of the world that would come to understand conceptual understanding of human consciousness. Everything was going well; Ryuji spent countless hours reading every piece of literature he could find that would eventually provide him with just enough to conduct his experiment and prove that his research wasn't just metaphysical but scientific.
For many nights your boyfriend wouldn't come home, he’d spend countless nights devoting himself to his search for answers—the proof that a realm existed between our world and the afterlife, he theorized it was called the Boarderlands. At first, you didn’t mind it, If anything you’ve always been nothing but supportive for his pursuits. With time, he grew more distant, colder and withdrawn. His placing his research above you. It hurt more than anything.
“Yuji..” you’d begin, gently pushing the threshold open. He’d been trapping himself inside the home office for the few days, hardly getting enough sleep, hardly eating. He moved for the sole purpose of keeping himself in shape. You would often hear the treadmill whirl to life after several hours of silence.
“Did you need something?”
He would look up at you fleetingly, before increasing the speed. You stood there, hoping he would look at you again, smile even.
“I was hoping we could…go for lunch?” You stepped closer, looking up at him. Beads of sweat pricked at his honeyed skin, his hair fell around face, his chest straining with every ragged breath.
“Can’t.”
He didn’t hesitate, never considered that maybe taking a break to spend some much needed quality time with his girlfriend was a good idea. You could feel your patience thinning.
“Would a day off really hurt? Just—even a few hours with me…?”
Your voice dropped, softened. For someone who had written several academic papers, you could hardly articulate the way he made you feel. Cast aside? No longer needed? No word was strong enough to express how you felt.
He didn’t answer.
He didn’t even flinch.
The treadmill hummed louder, mocking you with its steady rhythm. Everything just hurt.
“I’ve always supported you,” you tried again, quieter this time. “I always will. But I can’t remember the last time you looked at me and… saw me.” You swallowed, your throat tight with tears. “I miss you, Ryuji. I miss my boyfriend.”
He finally slowed the machine, but not because of your words. His body was simply done. He stepped off, breath harsh, muscles trembling from exhaustion—and still, he didn’t come to you. He reached for a towel instead, wiping sweat from his face like you weren’t standing right you heart ripping apart in chunks.
“I don’t have room to miss things right now,” he muttered, not cruelly… just honestly. And somehow that honesty stung worse.
Things.
Your chest tightened. This was not the Ryuji you knew. This was a monster created, a byproduct of obsession.
“This?" Your voice trembled, brows furrowing deeply, struggling to grasp if you even heard him right.
He nodded once.
That was it.
Conversation over.
You waited. Just for a second. Just long enough to see if he’d say your name. Reach for your hand. Look at you with even a fraction of the warmth he used to.
He didn’t.
So you stepped back. One slow, careful movement. Then another. The room felt colder when you left it, like warmth simply didn’t belong there anymore. The door clicked softly behind you—too soft for how loud the hurt felt inside your chest.
For a long moment you just stood in the hallway, staring at nothing, trying to breathe past the ache pressing against your ribs.
You had promised you’d stand beside him no matter how hard things got.
You just didn’t realize hard would look more like hostility. As the weeks went by you drowned yourself in things that gave you a sense of purpose. You went on walks, treated yourself and tried out new cafes. You even went on a mini haul, purchasing a ton of cute bras, tops, and jeans. You loved Ryuji, that never changed. When he'd be buried nose deep behind articles you would crack the door open, setting down a box of pastries and a cup of coffee from his favorite place. His efforts ceased, but yours? They never did. You often reminded yourself that love was patience. That eventually things would be okay, back to normal.
It was futile to hope.
It started as a whisper across campus. Rumors. Curiosity. The kind that traveled with wide eyes and hushed excitement. Ryuji had finally reached the stage of testing. He’d found someone—someone willing, eager even, to help prove his theory. She wasn’t reckless; she was fascinated. Brilliant in her own right. A final-year student who admired his mind, respected his work, believed in the possibility of a world suspended between life and death just as fiercely as he did.
She signed every form. Read every risk. She chose it.
And for a while, it looked like everything was going right.
Until it didn’t.
No courtroom followed. No angry parents screaming malpractice. No lawsuits dragging his name through the mud. She had agreed. She understood. The institution protected him because legally, they could.
But no policy could protect him from what happened inside his chest afterward.
Time itself froze.
He stopped sleeping. Stopped speaking. Stopped looking at the world like it was something he belonged to.
The guilt hollowed him out.
You tried to hold him. Tried to whisper that he hadn’t forced her, that she chose, that he never meant— He didn’t believe you. He didn’t believe anyone.
One night, he drove. His foot pressing harder and harder against the gas pedal, hoping for an impact that would end him. That would end the humiliation, guilt and shame that swallowed his existence whole.
He didn’t succeed.
The doctors said his body survived, but pieces of him didn’t. They explained things clinically—oxygen loss, spinal complications, neurological damage. Words that sounded sterile compared to what they truly meant:
Ryuji would never walk again.
He couldn’t look at you when he woke up. You couldn't eat, could hardly sleep or move from his side. He tried to end himself. You cried so hard and long, until you no longer could. You chest hurt at the possibility of losing him. You couldn't. For weeks you sat by his side, awake until fatigue knocked your body downwards. On the days you would allow your mind to wander, your thoughts drifted to the past. Your first date; the beautiful red flowers he gifted you, the bright smile on his face, the way the corners of his crinkled when you kissed his cheek at the end of your date. He was back home hardly able to meet your gaze, navigating a life that no longer felt like his own. You drove him to physical therapy. Promising him that you would always be here. You held his hand. Even when he tried to pull away. The tension between you began to ease. The months passed, and Ryuji became more capable of independence. Still ashamed, still withdrawn, but not entirely. He looked you in the eye when he spoke to you, your conversations grew longer. Eventually, the smiles you craved for so long returned—small at first, then genuine, the kind that reached his eyes.
He let you back into his world, slow at first but steady. He asked for your opinions on his research, shared ideas he hadn’t spoken aloud in months. The walls between you slowly fell away, replaced by something you had longed for.
One evening, after therapy, he quietly asked. ”Did you want to have dinner together? I'll order takeout some Yakisoba and Karaage...?"
You nodded, hardly able to contain the smile. He knew those were your favorites. That night, you drank so much sake, both drunk and laughing for the first time in many long months.
You finished stacking the last of the plates, grabbing a cloth to wipe the table one final time. Ryuji was busy folding up the empty takeout containers, focused on tidying his side, and you thought you had the space to move freely.
But the floor betrayed you. Your foot slipped, and before you could steady yourself, a sharp little gasp escaped your lips.
The next thing you knew, you were falling—landing clumsily against Ryuji’s lap.
You froze for a heartbeat, startled, realizing only then how close he had been. The warmth of him hit you immediately, the press of his body, the taut pull of his arms bracing you instinctively, and the quiet exhale of his breath.
You hadn’t even noticed him there.
His eyes softened, but there was a flicker of something raw—desire tangled with hesitation, frustration, and self-consciousness. His jaw tightened for a moment, as if weighing words against pride and the vulnerability he still carried from the accident.
“I’ll be fine,” he said, voice steady, controlled, almost casual—but the faint catch in the edge of it betrayed him. “You don’t have to… worry.” His fingers gently pulled at your sweatpants, his dark gaze piercing into your own. "The real question is can you take it?" He teased, tugging lower. Fuck, he was being so... "Mhm..." You nodded, not exactly trusting your own voice. He made your stomach turn and twist, a simmering heat pooling lower, and lower. "Then show me." He leaned back, comfortable against his seating. You nodded, swallowing thickly, your face heating as you stood up from his lap, carefully tugging down the warm fabric, feeling the cool air against your legs. His eyes followed every slight movement, down to the slow drag of your panties. You looked back up, face embarrassingly hot. "Yuji—" Your lips parted around a silent sound, watching him lock the wheels into place as he balanced himself against the arm rest, working on his own bottoms before sitting back down. Your mouth went dry, your eyes zeroing to his cock. You quickly looked away— he didn't even give you a moment to recover before pulling you close, his hands firm on your waist, adjusting you comfortably on his lap. "I said. Show me." His palms pressed against your hips. You whimpered, a sound so soft a smile curved at the corners of his lips. "What can't take it?" You shook your head, pressing your hands over his own on the arm rest, before slowly lining the flushed head of his cock against your hole. You felt him against you, warm, before your hips slowly press lower. He barely manages to stifle a low, strained sound, his head drooping low as his hand grip tighter against your hips. His jaw clenched tight, dark strands falling over his face as his chest heaves. "Fuck—so—tight." He manages, the veins on his forearms corded with the restraint of holding your in place, and allowing you to set the pace. Your own breathing his just as shaky, your much smaller hands squeezing at his wrist, a small mewl tearing past your lips as you try to sink lower, desperately trying to ease your body and fit more of him in. "You're really—nngh." He gently guides you lower, a small high pitched sound escapes you, your head dipping against his shoulder as you tremble. "Y-Yuji...i-it's really deep." His heart almost melts at how utterly fucked you are, he didn't even move yet, and here you were trembling and gasping for air when he wasn't half way through yet. His hand gently smooths over your back, angling his head to press kisses against your jaw and cheek. "It's been a minute, hm?" Firm palm gently squeeze your ass, pulling your body lower, urging you to take just a few more inches. You nod quickly against him, your arms wrapping tighter against his neck as you whine. "It's in my tummy..." You whisper, he could've easily missed the words with how quiet you were. "Yeah?" His voice is surprisingly gentle, his hands gently kneading at the soft swells, squeezing softly. "Mhm...is it." He stills for a moment, before you feel the warmth of his calloused palm traveled from your hip, and press against your stomach. "Oh, fuck."
He exhales feeling the slight bulge protruding from your warm belly. "I really am deep." You nod, leaking down his thick shaft, delirious from your size difference alone, and the heat of his palm against the outline of his cock. "You're taking it so well, aren't you?" You're so dizzy all you can manage is a pathetic keen, and a nod. " 汚いくらい濡れてる。" (so wet it's filthy)
He hums, the words alone make your head spin. " 'm sorry..." You burry your face deeper against his shoulder, a sharp sob escaping your lips when he rolls his hips upwards, the movement sudden, making your insides coil tight. "AH—" "Thought you could take it?" He tugs your bottom half lower, gripping your hips in place, before pulling you back up, the slick sounds of your gummy walls sucking him in were beyond filthy, making your face burn up as you gasped against his shoulder. "You like it when I use you?" His arms tense with ease push and pull of your him, fucking you against him. You can't do anything but whine, wrapping your arms tighter and tighter around him as he picks up the pace. " 聞こえる？" (you hear that?)
You nod, against him a strained yelp spilling past your lips when his palm lands rough against your ass. "さっさと答えろよ ! " (hurry up and answer)
Tears prick at the corners of your eyes, as you manage a choked response. "U-Uhuh...h-hear it..." He's so deep, fucking in and out of your cunt, his round tip pressing against the depth of cervix almost punishingly. You're beyond dizzy, your body uselessly flopping against his torso, babbling mindlessly as he uses your gushy insides. "Y-Yuji..." He wail, eyes hazy and fucked out, trying to clench around him. His hands roughly pull your hips down, and you're brain is much again, your muscles loose, a familiar wave rising higher and high. " もうイっちゃう… " (gonna come) Your voice is thin and breathy, your legs trembling around him as your face pressed deeper against his firm chest, small hand gripping tightly onto his strained biceps. " ほら、イって。" (come for me.)
A wave so overwhelming crashes over you, your stomach clenching as you whine breathlessly, trembling with the intensity of your orgasm, twitching as another wave passes over you. Ryuji groans deep in his throat, his jaw clenched tight pushing up hips up with the last of his strength, emptying himself inside of you, his muscles trembling with effort as he pants, his head pressing against your damn strands. "Oh fuck." He exhales, running a damp hand through his hair. Before gently rubbing his thumbs against your bruised hips. You softly wince, struggling to lift yourself off of him. He gently adjusts you, pressing a kiss to the top of your head. "You okay?" His eyes pass over your frame, thoroughly fucked, skin glowing with a sheen of sweat, your limbs turned to jelly. You nod weakly, still clinging to him. "Washing up is going to be a nightmare of it's own." He mutters, a small smirk cracking at the corner of his lips. "You know I love you right?" This time, a smile tugs at your lips, your eyes trailing up to reach his own. "Mhm, love you too." "Oh, trust me. I know."
You had shown it more times than he ever did. And he knew, he had a lot to make up for.