Chapter 4: The Strange New Teacher

Kai Arden didn’t know if he had introduced himself well.

He had never been a teacher before. His whole life had been spent on the battlefield, behind a rifle, under the command of Leonhard. He knew how to kill twenty people in under a minute. He knew how to neutralize a target silently. He knew how to survive in forests, in deserts, in the ruins of bombed-out cities.

But he didn’t know how to teach.

He didn’t know how to stand in front of a group of teenage girls.

He didn’t know how to make them interested in linear equations.

He didn’t know how to smile without looking creepy.

The chalk felt foreign in his hand. Different from a gun. Different from a knife. Different from a grenade.

Even when I killed Zero Vale, I wasn’t this nervous,Kai thought as he wrote his name on the board. His handwriting was neat—too neat. Like typewritten text. No style. No character.

Zero Vale. His sword nearly took my head off. But I still wasn’t this nervous.

Why?

Because when I was fighting, I knew what to do.

Now? I don’t know.

What did Leonhard do to me?

Why did I agree to come here?

Oh right. Because of those nine families.

Kai wrote down the first subject—Mathematics. All capital letters, just like his name. Not because he was good at math. But because Leonhard had said, "You can teach basic math, right? It’s easy. Addition, subtraction, multiplication, division. Even kids can do it."

Easy, he says.

This isn’t easy.

This is really hard.

Kai turned to face the class. Nine pairs of eyes stared at him. Some with curiosity—Mira, Aria. Some with suspicion—Ella, Iris, Nora. Some with pure disinterest—Eve, Luna. One with an empty smile that made Kai slightly uncomfortable—Fay. And one with fire in her eyes, as if challenging Kai to make a mistake—Rin.

Nine girls. Nine daughters of the nine rebels he had killed eight years ago.

Kai looked away. He couldn’t stare at them for too long. The guilt was still there. Still gnawing at his chest. Still making him want to run out of this room and never come back.

But I already made a promise.

"I will live. Not for myself. But for them."

My own words.

I have to follow through.

"Today we’re going to learn about..."Kai looked at the textbook in his hand. It was new—given by Reina this morning with a small note on the first page: "Don’t traumatize those girls. Just think of them as new soldiers you have to train. But without weapons. And without violence." Kai didn’t know if that was a joke or serious advice. "...linear equations."

Silence.

No response.

Rin yawned. Eve went back to typing on her laptop. Luna stared out the window.

Kai sighed. Then he began to explain. His voice was flat, as usual—no variation in tone, no emphasis, no enthusiasm. But he tried. He tried to keep his explanations simple. He tried to speak slower so they could follow. He tried to look friendly.

Like a normal teacher, he thought. What do normal teachers do?

Smile?

Yeah, normal teachers smile.

Kai tried to smile. He lifted the corners of his lips, showing a little teeth, and tried to look friendly.

His face felt stiff. Like the muscles in his face had never been trained to form that expression.

Rin Scarlet—the red-haired girl in the front row—frowned. Her face scrunched up like she was looking at something disgusting.

"Sir, your smile is scary,"Rin said. Her voice was loud, honest, without filter—as usual.

Kai stopped smiling. His face returned to being blank.

"Sorry."

Rin put on an unsatisfied face. "Don’t try smiling again, Sir, or I’ll have nightmares."

"Rin,"Ella scolded from behind.

"What? I’m being honest,"Rin defended herself.

Kai decided to ignore that comment. He continued his explanation. About variables, coefficients, and how to solve simple equations. Every time he mentioned a new term, he wrote it on the board. Every time he forgot what to say, he looked at the textbook.

Textbooks, he thought. I used to learn how to read battlefield maps. Now I’m learning how to read textbooks.

"So, if x plus 3 equals 7, then x is..."

"Four."

The voice was soft, barely audible. Came from the corner of the room.

Luna—the quiet girl with silver-gray hair—didn’t raise her hand. Didn’t look at Kai. Her eyes remained fixed on the window, on the leaves swaying in the wind.

"Correct," said Kai.

Silence.

Kai continued. He gave another example. Then another. Then another. He talked about x and y, about numbers moving to the other side of the equation, about plus signs turning into minus signs.

The lesson continued.

Kai started to relax a little. His shoulders weren’t as tense as before. His hands weren’t shaking as much when holding the chalk. His voice wasn’t as hoarse from nervousness.

Maybe this isn’t so hard, he thought. Maybe I can—

"Hmph."

A small cough.

One cough.

Not loud. Not long. Just once. Like someone clearing their throat because dust had gotten in.

But for Kai, that cough sounded like a bomb exploding.

His head turned toward the sound. His eyes narrowed. His pupils contracted. His hand holding the chalk stopped in midair.

Rin Scarlet—the red-haired girl in the front row—was covering her mouth with the back of her hand. Her face was slightly red, maybe from the dust flying from the classroom floor that was rarely swept.

She coughed,Kai thought. She coughed.

His brain worked too fast. Memories from the past surfaced without permission.

The battlefield. The northern forest. Rainy season. Biological attack. Invisible, odorless, tasteless poison gas. His teammate—Jesper—coughed once. Kai calmly said, "You’ve caught a cold, weakling." Three hours later, Jesper coughed again. Twice. Then coughed up blood. Then died in Kai’s lap with his eyes open and his mouth full of red foam.

She coughed. That’s the early symptom. I have to—

Kai didn’t remember when he started running.

One second he was standing in front of the board, chalk in hand, mouth half-open explaining about variables.

The next second he was beside Rin Scarlet, his hand grabbing the girl’s back.

"We’re going to the infirmary."

"Huh?"Rin stared at Kai with wide eyes. Her face changed from red from coughing to red from shock. "Sir, I just coughed—"

Kai didn’t listen.

He lifted Rin—picking her up from her chair as if she weighed no more than a sack of rice. Rin wasn’t a thin girl. She was athletic, muscular, her weight definitely not light. But Kai didn’t feel any weight at all. His adrenaline was working too hard.

Rin, being stubborn, naturally fought back. She pounded Kai’s back with her fists. She screamed. She cursed.

"Hey! Let me go! I’m fine! Put me down, you crazy man! I’m not kidding this time!"

But Kai was already running toward the door. His bag was left on the teacher’s desk. Chalk was still in his hand. The textbook fell to the floor as he ran past the desk.

"Rin just coughed, why is he carrying her?!"Mira shouted from her desk, half-laughing half-confused.

"Mr. Kai! Let her go!"Nora Vale stood up. Her hands were already clenched at her sides. Her eyes narrowed. Nora was ready to act, ready to jump, ready to protect her friend from this crazy teacher.

"I’m noting this, Sir!"Iris laughed. "I’m noting this as evidence!"

But Kai didn’t stop.

He left class IX-9 with Rin on his back, leaving eight other girls looking at each other with expressions ranging from shocked to confused to disbelieving to—in Iris’s case—laughing out loud.

Ella Virel could only stare at the closed door.

She sighed deeply.

Our new teacher is crazy, Ella thought.

Or... he’s hiding something.

Why did he panic so much over a simple cough?

Like someone who doesn’t know normal illnesses.

Like someone who has only ever seen deadly diseases.

Ella opened her notebook. On a blank page, under the name KAI ARDEN she had already written earlier, she added some words:

Panicked over a cough.

Scar on cheek.

Wrinkled suit, mismatched pants, crooked tie.

Doesn’t know how to smile.

Sent by Leonhard.

What’s his connection to Leonhard?

Who is he really?

Ella closed her notebook. Her eyes stared at the door.

The investigation begins, Ella thought. I’m going to find out who this man is.

And what he’s hiding.

The infirmary at Phoenix Academy wasn’t big. Just two folding beds with clean white sheets, a wooden medicine cabinet with peeling paint, a small wooden table with a sheet of patient attendance paper, and a plastic chair slightly cracked on the backrest. The walls were painted pale white, with posters showing first aid procedures that had started to yellow at the edges.

But for Kai, this room felt like an emergency operating room on the battlefield.

He opened the door with his shoulder—because his hands were busy carrying Rin, who was still struggling—and entered quickly. The air in the infirmary smelled of antiseptic and clean cloth. A familiar smell. A smell that reminded him of the dozens of times he had lain on emergency beds with gunshot wounds, stab wounds, blast injuries, and Reina cursing while stitching his wounds without anesthesia.

"REINA!"

Kai shouted. His voice echoed in the small room.

A young woman stood up from behind the desk. She was wearing a loose white jacket with sleeves rolled up to the elbows—revealing her muscular forearms covered in thin scars. Her black hair was shoulder-length, tied back halfway with a simple clip. A few strands of hair fell loose onto her face, but she didn’t care.

Her face was sharp—pointed chin, high cheekbones, firm eyebrows. Her eyes were dark brown, sharp, and full of wisdom that seemed beyond her age. Her skin was slightly dark, the color earned from too much time under the sun.

Reina.

The principal of Phoenix Academy.

And Kai’s former medical team member in the Grim Reaper.

She was also known as the Angel of War. A nickname given because she could save anyone’s life, no matter how dire the condition, in the most brutal way possible.

Reina blinked when she saw Kai carrying a student. Her eyes moved quickly—observing Rin’s position on Kai’s back, Kai’s panicked expression, and Rin still trying to break free.

"Kai?"

"I think this girl needs a lung X-ray!"Kai said with a deadly serious face. His eyes didn’t blink. Sweat ran down his temples, wetting the collar of his already wrinkled suit.

Rin Scarlet was still trying to break free. Her face was bright red—not from pain, but from anger and embarrassment combined.

"You’re crazy! Let me go! I can walk by myself! I already said—Rin just coughed! COUGHED! Not shot!"

Reina was silent.

She looked at Kai. Then at Rin. Then at Kai again.

"Lung X-ray?"Reina repeated slowly. Her eyes narrowed.

"Yes. She coughed."

"Cough?"

"Once."

"..."

Silence.

Reina sighed. She walked closer—her steps calm, unhurried. Her eyes observed Rin from head to toe. She felt Rin’s forehead with the back of her hand, checking her temperature. Not hot. Then she pressed Rin’s neck with two fingers to check her lymph nodes. Not swollen.

"You don’t have a fever,"Reina said flatly.

"But she coughed!"Kai interrupted.

"Once."

"That could be an early symptom—"

"OF WHAT?!"

Reina shouted. Her voice echoed in the small infirmary. Even Rin—the stubborn girl who wasn’t afraid of anything—flinched slightly. Reina had a different aura when she was angry. An aura that reminded everyone that she was the Angel of War—an angel who could save lives, but could also destroy.

Reina sighed deeply. She looked at Kai with a mix of annoyance and pity.

"She just has a normal cough, Kai. Because your classroom is dusty. The floor of class IX-9 is rarely swept. That’s all. No deadly disease. A normal cough. Do you understand?"

Kai was silent.

His hands were still holding Rin on his back.

"So she doesn’t need an X-ray?"

"NO!"

"Or to be hospitalized?"

"NO!"

"Or given a high dose of antibiotics?"

"KAI!"Reina pointed at the door with her index finger. Her face was red from holding back her anger. "Take her back to class. Right now. Don’t traumatize this girl on your first day of teaching. I don’t want to receive complaints from parents that the new teacher carried their child because of a normal cough!"

Kai blinked. Once. Twice.

Slowly, he lowered Rin from his back. The red-haired girl immediately jumped away like a wet cat. She stared at Kai with a mix of anger, shock, and deep embarrassment.

"Are you crazy, Sir?"Rin said. Her voice was still loud, but slightly trembling. "Carrying me to the infirmary for one cough? What’s wrong with you? My—I mean, my mom taught me self-defense from childhood, did you think I was easy to carry around like a baby? How rude!"

"Sorry," said Kai.

That was the third word he had said today. Maybe the fourth. He had lost count.

Sorry. Sorry. Sorry.

I think I say sorry too much.

"Alright, just get back to class!"Reina snapped, waving her hand. Her eyes stared at Kai with a stern warning. "And you, Kai. Don’t cause any more trouble. I don’t want to hear complaints on your first day."

Kai nodded. He walked out of the infirmary with Rin behind him—still pouting, still angry, still punching the empty air as if practicing the punches she would throw at Kai later.

Before the door closed, Reina leaned back in her chair. She stared at Kai’s retreating back. His raised sleeves, his stiff walk, and the way he held himself back from running.

You idiot, Kai,Reina thought.

Your war trauma is still severe, huh?

That girl coughed once, and you thought it was a biological attack.

Back then, on the battlefield, you saw too many people die from coughing.

Now, every time someone coughs, you go back to the past.

Reina sighed. She closed her eyes for a moment, then rubbed her temples with her fingertips.

I hope you achieve your goal, Kai.

I hope you can live a normal life.

But if you keep carrying students because of a normal cough... your journey is still long.

Reina opened her eyes. She picked up a pen and wrote on a small note on her desk:

"Kai—schedule a psychological evaluation next week."

Then she smiled slightly.

Or maybe I just need to lock him in this infirmary and not let him out until he’s sane.

Kai and Rin walked back to class IX-9 in silence.

The school hallway was empty. Other classes had already started their lessons. The sound of teachers explaining could be heard from behind closed doors. Occasionally the sound of students laughing, chairs being moved, or chalk on a blackboard could be heard.

Rin walked two meters ahead of Kai—she didn’t want to be close to that man. Her back was stiff, her shoulders rising and falling because she was still angry. Occasionally she looked back, glaring at Kai, then turned forward again.

Kai didn’t know what to say. He just followed Rin from behind, keeping his distance, not trying to get closer. His suit was getting more wrinkled. His sweat was increasing. His red tie was getting more crooked.

When the door to class IX-9 opened, eight pairs of eyes stared at them.

Rin walked to her desk with firm steps. She sat down, crossed her arms, and put on the most pouty face ever. That face seemed to say: "Don’t talk to me. Don’t look at me. I’ll be angry until doomsday."

Mira whispered something to Rin, but Rin just grumbled and looked away.

Kai stood in front of the blackboard. Chalk was still in his hand. The board still had half an explanation of linear equations that hadn’t been finished.

"Sorry,"Kai said for what felt like the hundredth time. "Let’s continue the lesson."

He began explaining again. About x and y. About numbers moving to the other side. About plus signs turning into minus signs.

But the atmosphere was different.

Awkward.

Rin wasn’t looking at the board. She was staring at Kai with a piercing glare.

Mira smiled, but her eyes were restless.

Aria bit her nails.

Eve typed slower than usual.

Luna stared at Kai longer than usual.

Nora wasn’t sitting at her desk—she was standing by the window, ready to act if Kai did something strange again.

Fay laughed softly, for no reason.

Iris smiled faintly, her eyes sparkling—she was enjoying this chaos.

And Ella...

Ella observed Kai from her desk.

Her eyes didn’t blink.

This man,Ella thought.

He panicked excessively over a normal cough.

Like someone who doesn’t know normal illnesses.

Like someone who has only ever seen deadly diseases.

A scar on his cheek—a cutting wound. A sword or a large knife.

His eyes are empty, but not dull.

Ella opened her notebook.

On a blank page, under the name KAI ARDEN she had already written, she added some sentences:

A cutting scar on the cheek.

Empty but sharp eyes.

Who is he really?

Ella closed her notebook.

She stared at Kai, who was explaining linear equations in a flat voice.

I’m going to find out,Ella thought.

One by one.

Nothing can be hidden from me.