I had just stepped out of the office building when the clock on my phone showed six in the evening.
"Exhausting…" I muttered softly as I loosened my tie.
Today wasn't a bad day, but it wasn't a special one either. The reports were finished on time, my boss wasn't nagging, and the train ride home wasn't too crowded. Still, there was one thing that made my steps instinctively turn in a different direction than usual.
I stopped in front of a small cake shop on the corner of the street.
The display lights were warm, and behind the glass, various cakes were neatly arranged. Chocolate tarts, strawberry cakes, cheesecakes—nothing out of the ordinary. Yet today, they all felt important.
"Ah… I almost forgot," I said to myself.
Today was Seo Ah's birthday.
I pushed open the shop door, the small bell above it ringing clearly.
"Good evening!" the shop attendant greeted me with a friendly smile.
"Good evening. I'd like to order a birthday cake," I replied.
"For how many people?"
"…Two."
The attendant nodded without asking further questions. I pointed at a simple chocolate cake decorated with white cream.
"That one is fine. And the message… 'Happy Birthday, Seo Ah.'"
"Alright."
While waiting, I stood still, staring at my own reflection in the display glass. A man in his twenties with tired eyes and slightly slumped shoulders. It felt strange, thinking about my life up to this point.
I live with my younger sister.
Just the two of us.
Our father died in an accident years ago. A brief phone call from the hospital. An apology spoken too quickly. After that, our home was never truly the same.
And our mother…
I took a deep breath.
She left.
Not because of illness. Not because of an accident. But because she chose someone else.
She left Seo Ah and me behind without a word.
Back then, Seo Ah was still little. Too little to understand why our mother's suitcase disappeared from the closet. Too innocent to grasp why the phone was never answered.
"When is Mom coming home?" she asked every day.
I still remember it clearly.
Seo Ah sitting in the living room, hugging her knees, staring at the front door.
I crouched in front of her and gently patted her head.
"Soon. Mom must be busy."
I lied. Over and over again.
Day after day, Seo Ah kept waiting. I comforted her. Made her warm tea. Stayed by her side until she fell asleep. Repeated the same words again and again until even they began to feel hollow.
One day, she stopped asking.
And somehow, that hurt even more.
I clenched my fist without realizing it.
Ever since she was little, Seo Ah had been frail. Fevers, dizziness, exhaustion. The doctors always said she needed plenty of rest. I knew that. Still, a part of me couldn't help but hate our mother.
I wondered if she left because Seo Ah was too much trouble.
If she got tired of having a sickly child.
I never asked her. Maybe because I already knew the answer—or maybe because I was afraid of being wrong.
From that day on, I made a vow to myself.
I would make Seo Ah happy.
Even if it was just me. Even if our life was simple. I never wanted to see that look of despair again—the gaze of a child waiting for someone who would never return.
"Sir, your cake is ready," the shop attendant said, snapping me out of my thoughts.
"Ah, right. Thank you."
I accepted the cake box carefully, as if what was inside was far more fragile than it looked.
On the way home, my thoughts kept drifting.
Seo Ah rarely went outside these days. After her health worsened a few years ago, she quit school and spent most of her time in her room—playing games, watching videos, quietly laughing at the screen.
People might call her a NEET.
I never scolded her.
As long as she could still smile, that was enough for me.
I stopped briefly at a red light, staring at the cake box in my hands.
"She's looked more cheerful lately," I murmured. "Maybe… she's finally starting to forget those things."
I remembered her expression recently. No longer gloomy. No longer staring blankly out the window. A few days ago, she had even said to me,
"Hey, want to play a game together tonight?"
I had chuckled back then.
"If I'm not too tired."
The light turned green. I started walking again.
To be honest, our life wasn't luxurious. I didn't have much savings. Our house was small. Sometimes I had to work overtime just to cover Seo Ah's hospital bills.
But I never complained.
As long as Seo Ah was okay, my life felt… enough.
I stopped in front of our door, took a breath, and unlocked it.
"Brother?" Seo Ah's voice came from inside.
"Yeah, I'm home."
I stepped in, took off my shoes, and lifted the cake box a little higher.
"Happy birthday, Seo Ah."
She froze for a few seconds, then her eyes widened.
"Huh? A cake?"
"Don't look at me like that. Once a year is allowed, right?"
Seo Ah smiled—a calm smile, not forced.
"…Thank you," she said softly.
At that moment, I knew.
I might not have anyone else.
I might hate the past.
But as long as my little sister could smile like this—
my life had never been meaningless.
We celebrated Seo Ah's birthday in the simplest way possible.
No big numbered candles, no special decorations. Just a small dining table, two plates, two plastic forks, and a neatly sliced chocolate cake. Seo Ah sat across from me, leaning forward slightly, her eyes focused on the slice in front of her.
"The cake's good," she said while chewing slowly.
"Thank goodness. I wasn't sure which flavor to get."
"You always buy chocolate," she replied lightly.
I chuckled. "Because you always finish it."
She didn't deny it—just smiled and kept eating. Just seeing that made my chest feel lighter.
We finished the cake without rushing. Once the plates were empty, Seo Ah pushed her chair back slightly and stood up right away.
"Brother."
"Hm?"
"We're playing, right?"
I knew what she meant even before she said the name.
Dungeon Master Online.
That game… I was the one who played it first. As a way to unwind after work. Seo Ah often sat behind me, watching the screen with curious eyes.
"Why does the castle look so weird?"
"Why does this monster walk in circles?"
"If you make your own dungeon, can you design it however you want?"
I answered as best I could—until one day she said, "I want to try."
From that moment on, she never stopped.
"Give me a second, I'll clear the table first," I said, gathering the plates.
"Later," Seo Ah replied quickly. "I've already logged in."
I glanced at her. She was already seated at the computer, her hair slightly messy, eyes sparkling as she stared at the login screen.
I let out a small sigh.
I knew I should tell her to rest. To not stare at the screen for too long. But seeing that expression… I just couldn't.
"Alright," I finally said. "But don't stay up too late."
"Yeah, yeah," she replied without turning around.
I sat at my own chair and turned on my computer. As soon as I logged into our accounts, the Tower of Ourolith appeared on the screen—a hundred-floor tower we had built piece by piece.
"Floor 57 went smoothly?" I asked while opening the status panel.
"Yeah," Seo Ah answered quickly. "Ophelia managed to wipe two parties today."
I raised an eyebrow. "Using Resonance at full capacity?"
"Yep. I tweaked her AI a bit. Now she syncs more with the environment. So if a party gets too noisy, the dungeon immediately ramps up the difficulty."
"…You're teaching players to be self-aware that way?"
Seo Ah giggled softly. "They need to learn to be quiet."
I smiled. That was just like her—detail-oriented, meticulous, far too serious about the things she loved.
"By the way," she continued, "do you think I should upgrade the Sub-Floor Guardian of Infinity?"
"Valeria?"
"Yeah. The movement loop's starting to get predictable for veteran players."
I thought for a moment. "Maybe don't change the loop itself—change the pauses. Add random delays. Not always two repetitions. Sometimes one and a half, sometimes three."
Seo Ah looked at me. "Oh… that makes sense."
She immediately wrote something down in her small notepad.
"And," she added, "for player dungeon invasions… do you prefer brute force or system sabotage?"
I chuckled. "You're really asking that on your birthday?"
"Exactly because it's my birthday," she replied casually. "I want good ideas."
I leaned back in my chair. "Depends on the target. Casual dungeons—brute force. But high-rank ones… sabotage. Destroy their resources first. Don't go straight for the core."
Seo Ah nodded slowly. "Then Eugene would be good to deploy."
"Void is always good," I said. "Just don't overuse it. Players get frustrated."
She smiled, satisfied.
"Oh, hey," she said again. "Did you check yesterday's event item?"
"The one from the Abyssal Clock raid?"
"Yeah. I got a weird drop. It's called Time-Locked Sigil."
I opened my inventory. "Ah, that one. I haven't used it yet."
"What a waste," she said. "If you combine it with Stasis, you can lock a floor for one real-time hour."
I glanced at her. "You're serious?"
"Yeah. But I didn't dare implement it without discussing it first."
I paused, then laughed softly. "You've gotten way better than me."
Seo Ah shook her head quickly. "No. I just… like thinking about this stuff."
I knew. This game wasn't just a game to her. It was a place where she could control something—where she didn't have to fear being left behind.
I stared at the screen. The Tower of Ourolith stood tall, filled with systems, guardians, and rules we had created together.
"Seo Ah," I said quietly.
"Hm?"
"As long as you're happy… keep playing. I'll be here with you."
She turned toward me. She didn't say anything for a few seconds, then smiled softly.
"Thank you, Brother."
We returned our focus to our respective screens, discussing legendary items, rare collections, and upcoming events as if the outside world didn't exist.
And for a moment—
our lives felt complete.