My phone vibrated on the desk with the frantic intensity of a system alert. I didn't even have to look at the screen to know who it was. There was only one person in my contacts who used that many exclamation marks.
​[18:42] Doyoon: HYUNG!!!!!!!!!!!!
[18:42] Doyoon: SHE SAID YES!!!!!!!!!!!!
[18:43] Doyoon: THE STRAWBERRY MILK WORKED! THE DATA PROCESSED! I'M OFF THE LOADING SCREEN! I'M OFFICIALLY THE LUCKIEST GUY IN SEOUL! ðŸ˜ðŸ˜ðŸ˜ðŸ™ŒðŸ™ŒðŸ™Œ
​I stared at the screen for a long beat. The "Integration Test" was over. My sister—the sharp-tongued, fiercely independent Harin—had actually let someone into her perimeter. And that someone was a boy who still tripped over his own feet and thought a Shakespearean tragedy was a slow Wi-Fi connection.
​I set the phone down, stood up, and walked across the hallway.
​I didn't knock. I pushed the door open to find Harin sitting at her desk, ostensibly doing homework, but her eyes were fixed on her phone with a look I had never seen before. It wasn't her usual mischievous spark; it was something softer, a quiet glow that made her look disturbingly like Danoh when she thought I wasn't looking.
​She jumped when she saw me, quickly flipping her phone face down. "Oppa! Ever heard of a thing called privacy?"
​I didn't answer. I just stood in the doorway, leaning against the frame, and stared at her. I looked at her as the person who had shared every meal with me, the person who had seen me at my absolute lowest, and the person I was prepared to protect against any threat—digital or physical.
​"What?" she snapped, though her cheeks were turning pink. "Why are you looking at me like I'm a bug in your code?"
​I remained silent for another ten seconds, letting the weight of the moment settle. I was analyzing the situation. My little sister was "in a relationship." The variable had been set.
​"Congrats," I said finally. My voice was flat, but I let a tiny bit of the tension leave my shoulders.
​Harin blinked, her defensive posture slumping. A wide, genuine smile broke across her face—the kind of smile that reminded me she was still the little girl who used to follow me around with broken toys. "Thanks, Oppa. He's... he's an idiot, but he's a good idiot."
​"He is a high-level idiot," I corrected. "But he's persistent."
​I turned and walked back to my room without another word. I had acknowledged the update. Now, I had to secure the firewall.
​I picked up my phone and opened the chat with Doyoon. The boy was still sending stickers of dancing bears. I waited for the flurry to stop before I typed out a single, precise message.
​[18:50] Hanbin: Listen carefully. You've passed the initial test. But if you ever make her cry, if you ever hurt her, or if you even think about being careless with her... I won't just delete your progress. I'll break your legs.
​The "Seen" icon appeared instantly.
​For three minutes, there was no reply. The dancing bears vanished. I could almost imagine him trembling on the other side of the city. Finally, a message came back.
​[18:54] Doyoon: Understood, Hyung. Clear as crystal. 🫡 I'll guard her with my life. Please don't break my legs, I still have taekwondo finals next month!
​I locked my phone and tossed it onto the bed.
​"Oppa!" Harin yelled from the other room, her voice sounding half-annoyed and half-amused. "Doyoon says you're threatening his physical safety! Stop being a creep!"
​"I'm just performing a security audit!" I yelled back.
​I sat back down at my laptop, but I wasn't looking at my code. I was thinking about the dinner we were supposed to have at Danoh's restaurant tomorrow. The whole group—Hyuk and Minah, Danoh and me, and now the two "idiots."
​My system was getting crowded. There were too many people, too much noise, and the emotional overhead was becoming difficult to calculate. But as I felt a strange warmth in my chest, I realized I didn't want to optimize it away.
​I opened a new tab and searched for: "How to act like a normal brother-in-law when you want to fight the boyfriend."
​The search results were inconclusive. I'd have to figure this one out manually.