Chapter 1: The Threshold of Unease
The key clicked in the lock with a sound that always felt too loud, like she was announcing an intrusion. Mizuki pushed the door open, the familiar scent of stale coffee and old cigarettes washing over her. Her smile, practiced and hopeful on the ride over, began to wilt at the edges.
“Suku, I brought those mochi you like—” Her voice died in her throat.
The apartment was a cave, dim and half-lit. The only illumination came from the flickering television, casting jumpy shadows across the worn leather couch. And on that couch, Megumi was sprawled like a cat in a sunbeam that didn’t exist.
She was wearing what looked like one of Sukuna’s old band shirts, the fabric thin and washed to transparency. It barely covered her thighs. Mizuki’s eyes, against her will, caught the faint, dark shadow of her small breasts through the cotton, the clear outline of her nipples. Below, she wore only a pair of black lace panties that left very little to the imagination.
“Kuna-nii, you’re back!” Megumi’s voice was a soft, delighted purr, completely ignoring Mizuki standing frozen in the doorway. She uncurled herself, the shirt riding higher, and padded across the floor on bare feet.
Sukuna dropped his keys on the side table. His face, which was usually a mask of bored arrogance when he looked at Mizuki, transformed. His sharp crimson eyes softened at the corners. A real, unforced smile touched his lips. “Making yourself comfortable, princess?”
“Your couch smells like you,” Megumi said, as if that explained everything. She wrapped her arms around his waist, pressing her cheek against his chest. His own arms came around her automatically, one hand settling on the small of her back, his fingers splaying possessively over the thin fabric of the shirt. He rested his chin on top of her messy black hair.
Mizuki stood there, clutching the paper bag of mochi. The handle bit into her palm. She was a statue in her own boyfriend’s apartment.
After a long moment, Sukuna finally glanced over Megumi’s head. “You gonna stand there all night? Close the door, you’re letting the heat out.”
The spell broke. Mizuki mechanically kicked off her shoes, her movements clumsy. “Hi, Megumi,” she forced out, her voice too bright, too thin.
Megumi half-turned her head, her intense blue eyes flicking over Mizuki with a detached coldness. “Oh. Hey.” She turned back into Sukuna’s chest, nuzzling slightly. “I’m starving, nii-chan. Did you get the spicy ramen?”
“In the bag by the door,” he said, his voice a low rumble Megumi would feel. He didn’t move to disentangle himself.
Mizuki bent to pick up the other grocery bag. She walked to the kitchen, a tiny alcove separated by a breakfast bar. She could feel their presence behind her, a single unit. She started unpacking the groceries with too much focus, lining up cups on the counter.
“You’re in my way, Mizuki.” Sukuna’s voice was right behind her. He’d finally detached from Megumi, who had slunk back to the couch and curled up, the television light playing on her bare legs.
He reached around her for a pot, his body pressing her briefly against the counter. He didn’t acknowledge the contact. “Make yourself useful and chop the scallions. Unless your delicate sensibilities can’t handle a knife.”
“I can handle it,” she murmured, taking the knife. The metallic shink-shink-shink as she sliced was the only sane rhythm in the room.
From the couch, Megumi let out a low laugh at something on TV. “Kuna-nii, remember this part? You said it was so stupid.”
“Still is,” he called back, his tone warm with amusement. “You have the worst taste in movies.”
“You watch them with me.”
“Someone has to. To mock them properly.”
Mizuki concentrated on the green circles piling up on the cutting board. Her eyes stung. From the onions, she told herself.
The ramen was a ritual. Sukuna cooked, movements efficient and rough. Megumi narrated her day from the couch in a lazy, intimate drone—who she saw, what some guy said to her, how boring her classes were. Sukuna grunted replies, asking sharp questions that showed he was listening to every word.
Mizuki set the small table for three. She put out napkins, adjusted chopsticks.
When the bowls were served, Megumi finally wandered over. She slid into the chair next to Sukuna, their knees bumping underneath the table. She wore the shirt like a dress, and as she sat, Mizuki saw a flash of black lace at the very top of her thighs.
“This is good, nii-chan,” Megumi said, slurping a noodle.
“Obviously,” Sukuna said, but he was watching her eat, a satisfied look on his face.
Mizuki picked up her own chopsticks. The food tasted like ash. “How was your day, Suku?” she asked, trying to claw her way into the conversation.
He shrugged, not looking at her. “Fine. Some idiots at work can’t follow basic instructions. The usual.”
“Oh. That’s… frustrating.”
“Astounding observation,” he deadpanned, finally flicking his gaze to her. It was empty. “Pass the chili oil.”
She did. Her hand shook slightly.
Halfway through the meal, Megumi dropped her chopsticks with a clatter. “Ugh, I’m full.” She leaned sideways, her body tilting until her head rested on Sukuna’s shoulder. One hand came up to rest casually on his thigh. “Your cooking is too filling.”
“Don’t waste it,” he said, but there was no heat in it. He picked up her bowl and started finishing her leftovers, an act of casual intimacy that felt more violating than anything else Mizuki had seen that night.
Mizuki stood up abruptly, the legs of her chair scraping the floor. “I’ll do the dishes.”
She fled to the sink, running the water too hot. She scrubbed the pot, the sound drowning out their low murmurs. The steam fogged the tiny window above the sink, blurring the city lights outside into glowing smears.
She felt him before she heard him. A presence at her back, radiating heat like a furnace.
“You’re quiet tonight.” His breath stirred the hair by her ear. It wasn’t concern. It was an accusation.
“Just tired,” she whispered, scrubbing a bowl that was already clean.
His hand closed over her wrist, stilling her. His grip was firm, not quite painful. “You’re being weird. It’s annoying.” He turned her around to face him, his crimson eyes searching her face with detached curiosity. “You got a problem?”
Over his shoulder, Mizuki could see Megumi on the couch. She was watching them, her expression unreadable in the flickering light. One hand was tucked between her thighs, the other holding her phone, but her dark blue eyes were fixed on them, on Sukuna’s hand on Mizuki’s wrist.
Mizuki’s heart hammered against her ribs. The words were a tangled mess in her throat: It’s her. The way she looks at you. The way you look at her. This isn’t right.
But all she could see was the cold assessment in his eyes, the impatience in the set of his jaw. He loved his little princess. To say anything would be to make herself the villain, the hysterical girlfriend who couldn’t understand a close sibling bond.
She swallowed the knot of hurt and confusion. It settled in her stomach like a stone.
“No,” she said, her voice barely audible. “No problem.”
He stared at her for a second longer, then released her wrist with a faint sound of dismissal. “Good. Don’t be so tense. It’s boring.” He walked back to the couch, dropping down beside Megumi. His sister immediately curled into his side, tucking her feet beneath her.
Mizuki turned back to the sink. She finished washing the last bowl, dried her hands meticulously, and walked back into the living room. They were like a painting, a study in dark intimacy. She was the errant brushstroke, the smudge that didn’t belong.
“I think I’m going to head home,” she said, her voice surprisingly steady.
Sukuna looked up, annoyed. “Now? It’s late.”
“I have an early shift tomorrow.”
He studied her, then shrugged. “Suit yourself. Lock the door on your way out.”
Megumi didn’t look up from her phone. “Bye, Mizuki.”
The walk to the door was a mile long. She collected her bag, slipped on her shoes. Her hand was on the cool metal of the door handle when she heard Megumi’s voice, a soft, giggling whisper.
“Kuna-nii, your girlfriend is such a mouse.”
And Sukuna’s reply, a low, fond chuckle. “Yeah. But she’s my mouse. Now shut up and watch the movie.”
The door clicked shut behind Mizuki, sealing her out in the quiet, dim hallway. The silence was deafening. She stood there for a long moment, leaning her forehead against the painted wood, hearing the faint murmur of the television from within.
Inside, everything was warm, entangled, complete. Out here, she was just clutching a purse, alone, with the distinct and chilling feeling that she had not just left her boyfriend’s apartment, but that she had never really been inside at all.