When Jungkook walks into the apartment, he sniffs the air and catches a burnt smell. He takes off his shoes, hangs his coat, and hears "Boogie Wonderland" blasting from the kitchen. This isn't Yoonji's style—she doesn't cook or listen to this music.

He walks into the kitchen, the smell of burnt becoming even more distinct. Then, he shifts his gaze to the table, where an unfamiliar guy is sitting. What the fuck?

"Who are you?"

The guy looks up and puts a finger to his lips, signaling him to be quiet.

Is he serious? Looks like a weirdo. Hair all messy, a pencil behind his ear, another one in his hand. He scribbles something on a piece of paper, then stops to sing along to the song, and resumes scribbling. God, what a weird dude. It's a shame he's so good-looking.

"Who are you?" Jungkook asks louder.

The guy looks up. "Huh?"

"Who are you?!" Jungkook raises his voice over the music.

"Taehyung."

Seriously? Taehyung. Okay. And?

Jungkook feels a touch on his shoulder. He catches a whiff of a familiar perfume. It’s Yoonji.

“Baby, don't mind him. It's my crazy brother. He just arrived from Germany today, and he's still looking for a place to stay.”

Jungkook sighs in relief. So, he's not some weirdo who broke into their home.

"And what's that burnt smell?" he asks.

"Oh, that's coffee. I made some. Help yourself if you want," Taehyung replies without looking up from his writing.

"Very kind of you, Taehyung," Jungkook replies, looking at the spilled coffee from the stovetop espresso maker. He glances back at Taehyung. He's busy writing, sticking his tongue out in concentration, then lifts the paper with a smile.

Oddly, Jungkook doesn't feel annoyed with this guy, even though he's created a mess in their kitchen.

The music keeps playing, switching from "Boogie Wonderland" to "September" by Earth, Wind & Fire.

Yoonji sighs loudly, and takes Jungkook's elbow, leading him into the living room.

"Sorry, Kookie. I had no idea he was even coming. He's always... unpredictable."

"I didn't know you had a brother."

"Sorry, he's just... Weird. We don't really connect. I love him, but... It's just really hard for me with him."

"He looks funny."

"No, he's not funny. He's batshit crazy, Jungkook. Stay away from him.”

But Jungkook wants to know Taehyung better. He does look kinda funny. After learning that Taehyung isn't some random guy who barged into their home, Jungkook feels both relieved and genuinely interested. He's never met someone quite like him.

Ignoring Yoonji's comment, Jungkook goes back to the kitchen. Taehyung is at the counter, pouring more coffee and doing a little dance.

"Taehyung, turn down the music. It's too loud," Yoonji says from somewhere behind him.

"Yoonji, 𝑚𝑒𝑖𝑛𝑒 𝐿𝑖𝑒𝑏𝑒, you know I can only focus when the music is blasting. I'm almost solving this problem!”

"What problem are you working on?" ask Jungkook.

"The P versus NP complexity classes." Taehyung shrugs, heading back to the table.

"I have no idea what that is, but it sounds cool," Jungkook remarks.

"Really?" Taehyung smiles, a beautiful smile. Jungkook finds himself thinking that he wants to see that smile more often.

"It's one of the central open problems in algorithm theory, an unsolved problem in mathematics."

“Seriously?”

"Yeah."

Yoonji sighs again. The last thing she needs is for Taehyung to drag Jungkook into something.

“Kookie, let's go grab something to eat?"

Jungkook feels his stomach growl. "Yeah, sure. Taehyung, you coming?"

Yoonji sighs once more, rolling her eyes. But Taehyung just nods, focused on his math problem. Yoonji sighs again, this time with a bit of relief.

Jungkook kinda enjoys having Taehyung around, bringing a bit of chaos into their too-perfect life. Taehyung tries to clean up the mess he makes - picking up papers (though sometimes they slip from his hands, and Jungkook finds a few scattered sheets on the floor)

Taehyung washes the coffee mugs (apparently, coffee is his main source of sustenance). If a thought strikes him, he might write something with a dry-erase marker on glass surfaces, but he almost always erases it afterward.

(unless he forgets, and Jungkook doesn't really mind). When Jungkook comes home, he often finds Taehyung lost in thought. He sits and watches because Taehyung can go a while without noticing him, but then he looks up and gives that weird but bright smile.

Jungkook likes it. He really wants to be friends with Taehyung.

This time, he sits next to him, peeking at Taehyung's notes. He doesn't understand a thing, but it's still interesting to watch. The music is blasting again, this time it’s Mr. Blue Sky. There are two coffee mugs in front of Taehyung—one full, the other half-full.

"Do you really like coffee that much?" Jungkook asks.

Taehyung shrugs, not surprised Jungkook joined him.

"Nah, I hate coffee. But my brain works better when I drink it."

Taehyung keeps surprising him. But that's why Jungkook likes him.

Another cute habit of Taehyung is that he sometimes talks to himself. Yoonji says it looks like he's talking to angels. Adorable.

"Wanna grab something to eat, Tae?"

Taehyung looks up at him again, resembling an owl. Why does Jungkook find everything he does cute?

"Tae? Can't remember the last time someone called me that."

"What do they usually call you?"

"Taehyung, Kim, crazy, Professor Kim, weirdo, Taehyungie - that's what my mom calls me. Oh, and asshole.”

Jungkook frowns. He's called Taehyung “weird” in his own head a couple of times, but it turns out Taehyung just lives in his own world. He's doing what he loves.

But being called "crazy" or "weird" constantly... it's sad.

"I can cook something if you want to eat," Taehyung offers.

Again, so kind of him. But the last time Taehyung tried to cook for him, he burned a toast. And a toaster.

"Thanks, Tae, but I'm in the mood for some Italian food today. There's a place nearby. Wanna join me?"

Taehyung pondered for a moment, looking up, then nodded.

"Yeah, let's go, why not. Just give me a minute to fix my hair, and I'm ready."

As it turns out, when Taehyung says he needs to "fix his hair," it simply means he tames a few unruly strands and shifts the pencil from one ear to the other.

They eat at the restaurant, and Jungkook notices how cutely Taehyung pouts as he eats.

Taehyung tells him about his work, research, and how he wants to solve all the unsolvable math problems.

Sometimes he grabs a napkin and writes down some thoughts, but then he returns to the conversation with Jungkook.

Jungkook is used to it by now, so he doesn't pay attention to how quickly Taehyung shifts his attention. He really enjoys watching him do what he loves to do.

And what Yoonji said? That's just not true. Taehyung isn't batshit crazy, he just lives in his own world.

Sure, Yoonji knows her brother better, but he seems harmless, except for the little chaos he brings.

Jungkook tries to bring up the topic with Yoonji, but she avoids it, hugging Jungkook, then biting and kîssing his néck.

Jungkook hesitates, not feeling that he’s ready for anything today. But he strokes her sides, then kísses her, seating Yoonji on his lap.

Then they hear a slam from the front door. Yoonji doesn't break the kīss, but Jungkook gently pushes her back by the shoulders.

Taehyung stands in the middle of the living room and just stares at them. Jungkook stares back at him.

"Don't mind me. I have a purely scientific interest in you."

Jungkook chuckles softly, resting his head on Yoonji's shoulder.

He feels Yoonji getting annoyed and strokes her sides.

"Tae, can you make me some coffee?" Jungkook asks.

Taehyung nods, then looks at Yoonji.

“Yoonji, 𝑚𝑒𝑖𝑛 𝐸𝑛𝑔𝑒𝑙, lovemaking isn't done with such a sour face."

Jungkook laughs, this time not so quietly.

Jungkook generally likes his job, but most of the time, it's pretty boring – paperwork, meetings with fake-friendly people, quarterly reports. But he can't complain, he makes good money.

Plus, his company's partners often set up meetings in fancy restaurants, so he gets to enjoy good food while talking business.

Right now, he's stuck filling out more paperwork when he'd rather be at the gym because his backside is feeling the effects of too much sitting.

But then there's a knock on the door. His secretary Yujin walks in.

"Mr. Jeon, someone is here to see you. They request a personal meeting right away."

Jungkook looks surprised. He doesn't have any appointments today. But feeling a bit bored, he says, "Bring them in. Thanks, Yujin."

And then he spots a messy head in the doorway.

"Hey, Tae. What are you doing here?” Jungkook asks.

Taehyung walks fully into the room and lets Yujin through, letting her walk out. He then closes the door behind her. Turning, he looks at Jungkook, takes out his notepad, and starts writing something.

Jungkook watches him with a questioning look. He notices that Taehyung isn’t paying attention to him and clears his throat. Taehyung lifts his head again and looks at Jungkook.

"I had this thought that if I want to solve the equation, I need to see you," Taehyung says.

And Jungkook smiles. He smiles and feels a warmth in his chest. An idea crosses his mind.

"Do you want to go to the conference room with me? It's free for the next hour, and I have," he checks his watch, "a break. It's soundproof, and you can play any music you want. It'll help you focus on the equation."

Taehyung looks at him very surprised. He has a highly expressive face, and it's so attractive. Jungkook thinks again about how beautiful he is. Then Taehyung smiles so warmly. Jungkook has never seen him smile like that.

"Yes, sure. I'd be very happy to. Thank you, Jungkook."