SISTER'S BOYFRIEND KSJ

Characters Introduction;-

YN (You)

Age: 21

Relationship: Seokjin’s secret lover — young, emotional, and deeply in love.

Kim Seokjin

Age: 32

Relationship: YN’s elder Sister's boyfriend — charming, protective, and madly in love with her.

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AUTHORS POV

The walls of their shared home had witnessed more than just silent grief and late-night tears. After their parents passed away a year ago, Choi YN and her elder sister Hana leaned on each other like two halves of a broken soul. The house wasn’t grand, but it was filled with warmth—books that still held their mother's scent, mismatched mugs from their father’s favorite café, and laughter they tried so hard to keep alive.

And then came Kim Seokjin.

He entered like spring after a cruel winter—gentle, soothing, full of sunshine. Hana met him through a mutual friend at work, and within months, his name lingered around the house like a soft perfume. His laughter echoed down the hallway, his shoes lined up beside theirs, and his voice, deep and melodic, became part of the air they breathed.

YN remembered the first time she saw him clearly.

It was a Sunday.

She had just come back from tutoring and entered the kitchen, sweaty and drained. And there he was—tall, radiant, wearing Hana’s apron and making ramyeon like he’d always belonged there.

He turned around and smiled.

“Hi, you must be YN. I’m Seokjin.”

Her world didn’t shatter then—but it cracked. Just a little.

She smiled back. “Yeah. I’ve heard about you.”

She had. Over and over. Hana would talk about him like he was the dream she never thought she'd get to live.

And YN? She listened. She always listened.

She never thought she'd fall for him too.

But she did.

Quietly. Slowly. Irrevocably.

It wasn’t just his looks—it was the way he treated Hana, the way he helped YN with her broken laptop without being asked, the way he made them both laugh until they forgot about the pain of losing their parents.

It was the way he made the house feel alive again.

But that made it worse.

Because he wasn't hers to want.

That evening, Hana had gone to meet a friend. YN sat on the small couch, curled up in her hoodie, pretending to read. Seokjin was sitting on the floor with his laptop, editing some presentation for work.

“You okay?” he asked, not looking up.

She blinked quickly. “Yeah. Just tired.”

He finally turned to her. “You’ve been quiet lately. More than usual.”

Her heart pounded. “I guess it’s just... stuff.”

“Stuff?” he raised a brow.

“I miss them. Mom and dad.” Her voice cracked, and it wasn’t a lie. She did miss them, but that wasn’t the only reason for the hollowness.

He got up and sat beside her on the couch without hesitation. “You don’t have to hold it in, YN. Not here.”

And she did break—just a little. A silent tear escaped her eyes, and before she could wipe it away, his hand was already there, thumb grazing her cheek softly.

“I hate seeing you like this,” he murmured.

You don’t even know you’re the reason.

He didn’t know her heart twisted every time Hana hugged him.

Didn’t know she stayed up at night, hating herself for what she felt.

Didn’t know that every smile he gave felt like a gift and a wound all at once.

That night, after he left for his. apartment, YN locked her door and fell on her bed, sobbing into her pillow.

She hated herself for falling for him.

She hated the universe for making it so hard.

She hated how gently he touched her shoulder, like he cared, and yet didn’t see.

And Hana? God, Hana was everything. Her sister. Her protector. Her only real family.

How could she ever hurt her?

She wouldn’t.

So she’d smile.

And break silently.

Again and again.

---

YN’s POV

I still remember him the very first time I saw him—how could I ever forget? It was late afternoon in autumn, and golden light spilled through the café’s tall windows in scattered patterns across the hardwood floor. I was curled up in a worn armchair by the counter, nose buried in a novel, trying to lose myself in someone else’s world.

And then I looked up.

He walked in like he belonged to the sunlight itself. He wore a charcoal-gray wool overcoat—long enough to brush his calves—over a crisp white shirt, the collar neatly pressed. His dark jeans were slim-fit but casual, and black leather Chelsea boots carried him across the cafe floor with an easy confidence. A soft cashmere scarf, the color of faded denim, was loosely draped around his neck, and I caught the faint scent of something warm—like cinnamon and cedarwood—whenever he passed.

He paused at the counter, tilting his head as if weighing the possibilities on the chalkboard menu. A barista called out, “Latte with oat milk, coming right up,” and he offered a slow, grateful smile—one that reached his eyes and made them crinkle at the corners. I couldn’t look away.

He turned then, and our eyes met for the briefest moment. Time dilated. I’d never seen anything so quietly magnetic: his dark hair, slightly tousled at the fringe; the gentle curve of his jaw; the way his shoulders relaxed as if he carried no burdens at all. My heart stuttered. And just like that, he went to find a seat—right at the table beside mine.

I pretended to read, but all I saw was the crease of his smile as he checked his phone, the strong line of his fingers tapping the screen. My pulse pounded in my ears, and it occurred to me how foolish I must look, staring at a stranger. But it didn’t matter. In that impossible moment, I fell in love—without knowing his name, without understanding why my chest felt so achingly full.

Later, when I told Hana about the “mysterious café guy,” she brushed it off with a laugh and said, “Probably someone from work, YN. I’ve met so many people lately, you’d lose track.” And every time I asked for a photo or a name, she’d change the subject—sometimes with a vague promise to show me “later,” sometimes with gentle teasing, as though I was silly to care.

So I never saw his face again—until months later, when Hana brought him home for dinner. I came down the stairs in my favorite soft sweater—light gray with little cable-knit pearls—and froze. There he was, carrying a bouquet of lavender in one hand and smiling exactly the way I’d memorized him in that café. Only now I knew him as Seokjin, my sister’s boyfriend.

My heart cracked then, a painful echo of its first, secret fall. All those afternoons I’d spent tracing his outline in my mind, wishing to know him… and all that time, he was just a few rooms away from me, entirely out of reach.

---

YN’s POV

Rain tapped softly against the windowpanes like fingers trying to find their way back inside. The house was warm, dimly lit, and quiet—too quiet for a Friday evening. Hana had ordered takeout, and now she sat beside me on the living room floor, two steaming cups of ginger tea sitting untouched between us.

“I found one of dad’s old hard drives,” she said, holding up the small black device like it was a treasure.

My breath caught. “The one with all the videos?”

She nodded, eyes already misty. “I thought maybe… we could watch a few?”

I didn’t say anything. Just nodded. Because if I spoke, my voice would break.

She connected it to the TV. A few folders blinked to life, all labeled in dad’s neat handwriting—Vacay 2015, New Year’s 2018, Random Home Vids, and one simply named My Girls.

Hana clicked on it.

And just like that, we were pulled into another time.

The screen filled with laughter. Our younger selves—messy-haired, bright-eyed—ran around the garden while our mom held the camera, her laughter unmistakable. Our dad’s voice was in the background, cheering us on. We watched as the two of us chased soap bubbles, completely unaware of what life would take from us one day.

Then came the birthday clip. My 13th. I knew exactly what was next.

The screen panned to a tall, slightly lanky boy with a wide boxy smile and wild black hair poking out from under a cap.

Taehyung.

He wore an oversized yellow hoodie, cake frosting on his cheek, and held up a handmade birthday card that looked like a 5-year-old designed it.

“I made this,” he said proudly in the video, handing it to me.

“Looks like a kindergartener made it,” I teased in the clip.

“You love it,” he said with a smirk. “Because I know your brain better than your diary does.”

And I had laughed, cheeks turning pink.

Sitting here now, years later, I hugged my knees to my chest and stared at the screen as if I could reach inside it, back into that moment, and hold it tighter.

Hana glanced at me. “You miss him.”

I nodded slowly. “He just... always knew when I wasn’t okay. Without me saying anything.”

“Like magic,” she whispered.

“Yeah,” I said, eyes still on the screen.

“Like magic.”

Taehyung had left for the U.S. two years ago—on a scholarship so big even the newspapers wrote about it. We promised to stay in touch. And we tried. For a while. But life pulled us into different lanes, and suddenly weeks became months, and his contact faded into a ghost on my screen.

And when mom and dad passed… he didn’t even know. I never told him.

Not because I didn’t want to—but because I couldn’t bear to make the

words real by saying them to him.

The next video played—one from a family picnic. And that’s when Seokjin appeared on the screen beside me. He wasn’t in the video, of course. He was in the room now. He’d arrived while we were watching, holding a box of cinnamon rolls from his favorite bakery.

“I brought—” he began, then stopped. His gaze landed on the TV.

“Oh,” he said softly. “Is this…?”

“Our parents,” Hana said with a smile, beckoning him to sit. “Come, watch with us.”

He sat beside her. Not beside me.

But I still felt his presence, like gravity shifting in the room.

He leaned forward slightly, resting his elbows on his knees, eyes focused on the screen. I glanced at him from the corner of my eye—he looked different in this lighting. Softer. Not as sharp and golden as that café afternoon, but warm, grounded. Real.

And still... unreachable.

My chest ached. Not just because of him, but because everything felt like slipping sand.

I missed our parents.

I missed Taehyung.

I missed the version of me that didn’t have to pretend she was okay every single day.

Later, when the video ended and the room returned to silence, Seokjin looked at me.

“You were always smiling in those videos,” he said gently.

I tried to laugh. “Yeah. That version of me didn’t know what life was planning.”

He looked like he wanted to say something—maybe comfort me, maybe ask more—but Hana leaned against him, resting her head on his shoulder.

And just like that, whatever moment might’ve existed between us dissolved into the air.

I looked away.

And quietly, I missed Taehyung even more.

---

AUTHOR'S POV

Late Night. 12:42 a.m.

The house was mostly dark, with only the hallway light faintly glowing under the bedroom doors.

Seokjin sat on the edge of Hana’s bed, his hand gently brushing her hair as she slept peacefully beside him. She’d fallen asleep mid-conversation, exhausted from the emotional weight of watching the family videos. Her soft breathing filled the room with quiet comfort.

He smiled, brushing a strand of hair from her face. “Sleep well, love,” he whispered.

Carefully, he got up, making sure not to wake her. He thought maybe he could fix something light in the kitchen—warm soup or grilled cheese. Just enough so it’d be ready when she woke.

As he stepped out of the room, his hand froze on the stair rail.

A sound—soft, muffled.

Crying.

He turned toward the direction it was coming from.

YN’s room.

His heart clenched.

He didn’t think. His feet moved on their own.

The door was slightly ajar. And through the narrow crack, he saw her—knees pulled to her chest, face buried into a framed photo, shoulders trembling with quiet sobs. Her long dark hair fell across her arms like a curtain, and her lips quivered as she tried to hold back the sound.

Something inside him ached.

Gently, he knocked once. “YN...?”

She looked up, startled. Her eyes were red, cheeks wet, and she quickly wiped her face, trying to pull herself together.

“S-Seokjin? I didn’t… I didn’t know anyone was awake.”

He stepped inside slowly, hesitating near the doorway. “I heard you. I was in Hana’s room… she fell asleep, so I came down to cook something. But—then I heard you crying.”

She looked down at the photo still clutched in her hand. It showed her, maybe six or seven years younger, standing between her parents. And beside her, smiling wide in a ridiculous leopard hoodie, was Taehyung.

Seokjin’s brows furrowed. He moved a little closer, eyeing the image with quiet curiosity.

“That’s… Kim Taehyung?” he asked slowly.

YN’s head snapped up. “You know him?”

He nodded, lips parting in realization.

“He’s Namjoon’s little brother.

Namjoon’s my best friend… we’ve been friends since college.”

Her breath caught.

The boy she’d missed for years. The one who had once been her shadow, her secret diary with legs, her peace. And now—he was connected to the very man who made her heart ache in ways she couldn’t name.

She blinked. “You’re… friends with Namjoon Oppa?”

Seokjin chuckled. “Yeah. Tae was just a kid when I used to go over. He always had this wild energy—constantly dancing, singing, teasing Namjoon to death.”

YN gave a small, tear-soaked laugh. “That sounds like him.”

Seokjin knelt beside her bed now, his voice gentler. “He meant a lot to you, didn’t he?”

She nodded. “He… he knew me. Not just the smiling parts. Even when I was quiet or pretending, he always knew when something was off. After our parents passed… I didn’t have the strength to reach out. And he never came back. I just… thought he forgot me.”

Seokjin’s expression softened.

He looked at her the way someone looks at a shattered vase—carefully, afraid to add to the cracks.

“YN…” he said after a long pause, “Would you like to talk to him?”

She stared at him. “What?”

“I can ask Namjoon. I’m sure he knows where Tae is. He might even have his number. If it’ll help… I’ll try to reconnect you two.”

She blinked rapidly. “You’d do that?”

He smiled, gently. “Of course. If it brings even a little peace to you, I’ll do it.”

Tears welled again—but this time, they weren’t just from grief. They were from the unexpected warmth in Seokjin’s voice. The tenderness in the way he looked at her—like she mattered.

“Thank you,” she whispered, voice cracking. “I’ve missed him so much.”

“I know,” he said softly. “And you’re not alone.”

He gently squeezed her shoulder—lingering for a second longer than he should have. A second too long for her heart to ignore.

She nodded, holding the photo tighter to her chest.

And just like that, the silence between them… didn’t feel so empty anymore.

---

It had been three days since Seokjin gave her the number. Three whole days YN spent staring at it on her phone screen like it held the key to something sacred. Her thumb hovered over the call button more times than she could count.

But tonight, with her heart full and her walls crumbling, she finally pressed it.

The phone rang.

Once. Twice.

And then—

“Hello?”

That voice. That deep, slightly raspy voice she hadn’t heard in years.

“Tae…” she whispered.

Silence.

Then a soft, shaky laugh. “YN? Wait—is it really you?”

A single tear slipped down her cheek. “Yeah. It’s me.”

And then everything she’d held in—every ache, every silent heartbreak—came flooding out in waves. She told him everything. About their parents.

About the loneliness. About Hana.

And then… about Seokjin.

She told him how she saw him before Hana ever introduced him. How she fell for him without knowing who he was. How she stayed silent out of love for her sister. How her heart was breaking from all the things she couldn’t say.

Taehyung didn’t interrupt. He just listened. The same way he always had. As if her pain was his own.

When the call ended, her chest felt lighter—but only slightly.

Until the next evening.

When he walked through the front door, she didn’t need a second to recognize him. He’d grown taller, broader, more refined in the way he moved—but the warmth in his eyes was the same.

“YN,” he breathed.

She didn’t speak.

She ran to him.

Their arms wrapped around each other like puzzle pieces finally falling into place. Her hands gripped the back of his hoodie. Her face buried in his chest. And she broke—just like she always did—with him.

“I missed you so much, Tae…”

“I know, sweetheart. I missed you too.”

Behind them, Hana stood near the hallway, hands covering her mouth as tears welled in her eyes. She hadn’t seen Taehyung since before their parents died. She moved toward him slowly and wrapped her arms around him from the side.

“You came back…” she whispered.

Seokjin stepped forward too, a surprised but genuine smile stretching across his face. “Tae,” he said softly, “It’s been a while.”

Taehyung pulled back and smiled as he hugged Seokjin too. “Hyung. It’s been too long.”

The moment was bittersweet—a family piecing itself together in silence, with unspoken grief and grateful reunions.

Later that evening, YN led Taehyung upstairs to her room.

It hadn’t changed much. A few new photos here and there. Her favorite blanket still draped over the reading chair. Soft fairy lights flickered on her wall, and the framed photo of her and Taehyung sat proudly on the shelf near her books.

They sat on her bed—side by side. A small plate of cookies between them. The comfort of familiarity wrapping around them.

They talked for hours.

About college. About life in the U.S.

About how hard it was for her to smile without pretending.

About how Seokjin always made it worse, and somehow better.

About how she hated herself for what she felt.

Taehyung listened.

But then, in a moment of soft stillness, he turned to her. His voice quiet.

“YN,” he said. “You love Seokjin hyung,so much don’t you?”

She froze.

Her lips parted, but nothing came out.

Taehyung didn’t rush her.

And she couldn’t hold it anymore.

Her shoulders shook as she broke down beside him. Sobs tore through her chest, raw and unfiltered. It was the kind of cry that came from carrying too much for too long.

“I—I didn’t mean to, Tae. I didn’t try. I just—he was there, and I felt seen. And safe. And then I found out who he was and it just—” She choked, “It hurts so much, Tae. And I can’t tell anyone. Not Hana. Not him. No one.”

Taehyung didn’t say a word.

He pulled her into his arms and held her tightly, his hand cradling the back of her head.

“It’s okay,” he whispered. “You don’t have to explain. I know your heart.”

Her fingers clutched his hoodie again, just like years ago. “Why does love have to feel like this?”

He let out a breath, pressing his chin lightly on her hair. “Because sometimes, the heart chooses before the mind can catch up.”

And in that moment, she let go. Of her shame. Of her silence. Of all the pain she’d buried just to protect everyone else.

Because Kim Taehyung, the boy who once understood her without asking—still did.

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STAY TUNE FOR PART 2 OF THIS.......