Kai is sitting on the sofa, numbly flipping through TV channels. After Hana’s outburst, Sehun immediately barged after his sister.

Leaving Kai to sink to the couch in shock.

    The possibilities began entering his mind in a flurry, everything that he could obtain with Hana’s secret. He could blackmail her into giving him stellar grades in her class, of course. But Kai is vying for revenge above all. Not just for himself and the other students who have suffered her hell-like Calculus class.

No, Kai wants revenge for Sehun as well.

    It is a drab October morning. Kai is convulsing with fits of sneezes as his chauffeur drops him off at his high school. Darn these disgusting allergies. Maybe Sehun has some Claritin, even though they're technically not supposed to bring it to school. What does the school administration think they're going to do? Crush up the tablets and snort them like ? Kai cares more about his dying sinuses than getting high off allergy medicine, thank you very much.

Kai trudges to the locker room so he can get changed for Physical Education. Strangely, the normally punctual Sehun is nowhere to be seen. Where could he-

"You guys!" Min Daeyoung, a classmate, flies into the room. Everyone looks up."Sehun's in the hospital! He tried to kill himself by overdosing on pills!"

To say that Kai's world goes crashing down around him is an understatement. Kai literally collapses to the hard vinyl floor of the locker room, his entire body trembling uncontrollably.

No. This cannot be true. Why would his upbeat, kind best friend be driven to attempt suicide?

Was it something Kai did?  Is this his fault?

Without another pause Kai scrambles up, blindly sprinting out of the locker room.

“Why?” Kai whispers as he stands over Sehun’s hospital bed. His best friend is lying on a standard cot, an IV tube attached to his wrist. Only his head peeks out from under the white sheets, looking up apologetically at Kai. “Sehun, what’s going on? Tell me the truth! I want to know!”

Sehun closes his eyes, exhaling hard. “I... it’s... my family.”

“What did they do? Did they hurt you? Why you didn’t tell me anything?!”

And Sehun explains everything to Kai. How he has been shunted aside by his parents his entire life because of his prodigy of a little sister. How his parents constantly harass him for not being as talented as her, how every other adult sneers at him for being the normal sibling. Sehun has never gotten anything he has wanted in his life; his sister, on the other hand, gets anything she asks for with a snap of her fingers.

Ever since his sister was accepted to MIT 2 years ago, Sehun’s parents have remained in America most of the year. They never call to ask how he is; when they do, it is brief and apathetic. His accomplishments are disregarded.

Sehun is not needed.

So why continue to live?

Kai is burning with rage, directed at Sehun’s entire family. But especially the despicable girl who caused Sehun’s life to be such hell. Kai has never met Sehun's sister. But he hates her. Hates her so much he can feel his body shaking with enmity.

Sehun fully opens up to Kai. He gradually recovers as time passes. Kai takes him to therapy sessions every week, and they always get burgers at the restaurant down the street afterwards. Not long after, they attend their first dance competition and win 1st place. Sehun's therapist approves of the boys' new hobby. She says dancing will be a healthy outlet for Sehun's depression.

Kai and Sehun are like brothers, inseparable.

It is not until a few months after Sehun recovers and is released from the hospital that Kai realizes:

Sehun’s parents didn’t visit him once.

    Hana drove Kai’s best friend to attempt suicide.

And now he can make her pay, in the worst ways possible.

    The door opens, and Sehun walks in... followed by her. Kai forces a smile onto his face and stands up.

    “Hey, you got her.” Kai runs a hand through his hair, avoiding Hana’s accusing, slightly red glare. “Hana, I’m sorry about what I said. I... really am. Actually, I have a lot of explaining to do about... everything.” He turns to Sehun. “Can you give us some privacy? I want to talk to Hana alone.”

    “Of course.” Sehun flashes Hana a grin that says, See? What did I tell you? “I’m going to go take a little walk. Then we can get started on dinner. Hana, I can’t believe you actually made all that food.”

A slight smile appears on Hana’s face.

    The instant Sehun has shut the door to the apartment, Kai has grabbed Hana by the hair and pinned her to the wall.

    “What are you doing?!” Hana shrieks. “You’re hurting me, let go!”

    “Not a chance,” Kai hisses. “Listen, . From this instant on, you’re doing everything I tell you. And I mean everything. Otherwise your little secret gets leaked out to the entire school.”

    Hana’s mouth is opening and closing like a goldfish. “Wha-you- are you blackmailing me? It won't working. You think the school administration doesn’t know my real age?”

    Kai’s lips curl up into a dangerous smirk. “The school administration might. But what about the parents? Would they really approve of a pissy little 19-year-old terrorizing their poor kids?”

    “How dare you.” Hana responds coldly. “You don’t understand how intelligent I am. When the parents find out their students teacher is a girl who earned her phD in 3 years, they’ll be begging for me to keep teaching their children.”

“Other parents might.” Kai lowers his lips to Hana’s ear. “But I know my parents won’t.”

A cold shock flies through Hana’s body. She knows it is his parents that yield the power to dismiss her in an instant. Hana is as good as dead if a single word of complaint reaches Kai’s family.

    “Why are you doing this?” Hana demands. “Is this because of my teaching style? I have a reason for doing it-,”

    Kai cuts her off. “Don’t try to make excuses for being a complete . You deserve this.”

    “Oh, really?” Hana lets out a dry, humorless laugh. “Well, I’m telling Sehun- ah!” Hana lets out a sharp gasp of pain as Kai pulls her hair harder, pressing her tighter to the wall.

    “You will not do anything of the sort,” he growls in an eerily chilling tone. “If you do, I’ll make him turn on you. He likes me better than he likes you, trust me. And besides... Sehun is a reason why I’m doing this.”

    Her jaw goes slack in an instant. Hana's body weakens as her head slumps to the side.

“So this is karma, I suppose,” she utters slowly. “What I get for something that wasn’t even my fault. Do you think I asked to be born with intelligence? Or asked my parents to enroll me in every competition they could, give me an IQ test, send me to MIT? This isn’t fair.”

    “It wasn’t fair for Sehun, either.”

    “Don’t you think I get enough with all of you in class?” Hana murmurs. “Writing those things on the tests, despising my every pore, cursing me behind my back and turning everyone against me?”

    Kai narrows his eyes. The formerly hardy, forceful Professor Oh has dissolved into nothing more than a broken teenager, defeated and crushed. The pang of victory Kai feels for affecting her seemingly indifferent exterior is smothered by a strange sense of pity.

It’s 100 students versus one girl that’s 2 years younger than us, he realizes.

    But she started it.

    “If you hadn’t acted so horribly, then it wouldn’t have had to come to this,” Kai says coolly. “Now get up. Sehun will be back any moment. Do you understand our deal?”

    Hana looks up at him, and Kai can see some of the old fire in her eyes blazing again.

    “I understand,” she responds in an incensed voice.

    “Now smile, so we don’t look suspicious.” Kai releases her from his tight grip, and leads her to a sofa. A wide beam appears on his face. “Hana. I’m glad we finally got everything figured out.”

    Hana stares at him emotionlessly.

    Still grinning, Kai says, “I thought you said you understood our deal, Hana.”

    A smile appears on Hana’s face. Her eyes remain stone cold.

    The door opens at that moment, and Sehun strolls in. His eyes curve up into crescents when he sees his sister and his best friend sitting together, laughing with each other.

    “I’m happy you two were able to resolve everything,” he sighs contentedly.

"Yes, I'm happy as well," Kai smiles.