I learned

The next day, 5:57 AM

Yu Chen had already woken up before the clock tower at Linxia No. 1 Middle School struck six times.

She wasn't woken by the alarm clock, but by the pain in her right hand's knuckles. The black bandage was wrapped too tightly, and overnight, blood had swelled into small pools at her fingertips. She sat up, used her teeth to tear open the Velcro strap, and the strip of cloth hissed as it came loose, revealing the bruised and greenish joint underneath—like a copper coin soaked in rainwater.

The dormitory curtains weren't fully drawn, and the first rays of morning light pierced through the gaps, falling on the textbook "Required Course 4" beside her pillow. A crease had appeared on the spine from her pressing it down last night, like a scar that refused to heal. Yu Chen picked up the book, gave it a shake, and a sticky note fell out—

An Yi's handwriting, written in pencil, was extremely faint:

Before morning reading, on the second floor of the library, seat A-17.

Trigonometric functions, Section 1: Radian measure.

An hourglass was drawn behind the writing. Ink dripped onto it and was erased by the eraser, making it look like it collapsed prematurely before it could take shape.

She stared at the words for three seconds, crumpled the note into a ball, and threw it into the trash can. The paper ball hit the side of the can with a "thud," like a referee ringing a bell: Round two begins.

6:10 AM

The playground was still shrouded in mist, with dewdrops clinging to the tips of the grass, like shards of broken glass scattered on the ground.

Yu Chen, wearing an old short-sleeved shirt from the sports school, her bright red hair casually tied back with a black hair tie, ran counter-clockwise along the track. On her third step, she heard another breath behind her—light, steady, yet deliberately heavy, as if offering her a heartbeat.

Shengshuo.

He wasn't wearing his school uniform; his white cotton T-shirt clung to his chest in the wind, and the silver "SS2023" embroidery below his collarbone was stained dark with sweat. The two stood side by side, their shadows blurred in the mist, like two running tracks yet to meet.

"Ten minutes." He raised his wrist, the watch face flashing coldly. "I'll measure your heart rate. The provincial team selection threshold for aerobic exercise is 160."

Yu Chen didn't slow down, but simply extended her right fist and gently bumped it against his arm—it was the secret signal she used to time him when they were kids at the sports school. Sheng Shuo pressed the button on his watch, and the second hand ticked, as if locking the air.

On the final lap, she sped up, her bright red hair bursting in the fog like a small fire against the wind. At the finish line, he pressed pause: 9'48", heart rate 162.

"You've crossed the line." His voice was low, but with a smile as he held the watch face up to her eyes, like handing her a pre-written, perfect answer sheet.

Yu Chen bent over, hands on her knees, beads of sweat dripping from her eyelashes and landing on the track, splashing up tiny sparks of dawn. She caught her breath and asked, "Did An Yi send you?"

"No." Sheng Shuo reset the watch, his voice muffled by the fog. "I asked him to write you a note."

Yu Chen looked up, and the morning sun, shrouded in mist, hung between them like a whitish iron coin. She reached out and wiped his sweaty palm on the hem of his T-shirt, leaving a dark watermark, like erasing an answer into a blank.

"Thanks," she said, turning to walk back to her dorm. "Don't wear a watch next time, or I might break it."

7:05 AM

Second floor of the library, A-17.

An Yi was already there. An A3 sheet of draft paper was spread out on the table. On the left was a trigonometric unit circle, and on the right, in the blank space, was a timeline drawn—marked with a grid every 5 mm, with "punch," "step back," and "feint" written next to it.

He broke mathematics down into rounds.

Yu Chen placed her water glass on the edge of the table with a "thud." Half a glass of cold glucose water swirled in the transparent glass, its color like diluted sunset. She sat down, pulled out a chair, and the wooden legs dragged across the floor with a "rip"—like tearing a hole in the air.

An Yi handed her a note:

"Radians, 180° = π rad."

Three minutes later, I'll give you the degree, you give me the radians, one mistake and you're done—"

There was no text written on it, only a drawing of a boxing glove with the words "10 push-ups" written next to it.

Yu Chen raised an eyebrow, flipped the note over, and added a line below the boxing glove with a pencil:

"If I make a mistake, you have to run 5 kilometers with me."

An Yi stared at the line of text for two seconds, and for the first time, a real crack appeared at the corner of his mouth—like ice being struck by an ice axe, the cracks spreading from the corner of his lips to his ear.

“Begin,” he said.

60°.

"π/3".

225°.

"5π/4".

-330°.

-11π/6.

...

Fifteen rounds, zero mistakes. An Yi's pen hovered at the last line, not falling. He looked up; the morning light fell on the ends of her bright red hair, like gilding the edges of a flame with a cold hue.

"Now it's my turn to test you." Yu Chen turned the draft paper around and drew a coordinate system in the blank space. She wrote "You" at the origin, "Provincial Team" on the positive x-axis, and "College Entrance Examination" on the y-axis. She randomly marked a point in the first quadrant with her pen: "Suppose this is the landing point of your opponent's right hand punch, tell me, which trigonometric function line can determine the distance the fastest?"

An Yi lowered his eyes, his eyelashes casting two cold, sharp lines on his eyelids. He took a pen, drew a line segment between the point and the origin, then drew a perpendicular line, and wrote:

"cosθ = adjacent side / hypotenuse. To find the hypotenuse given the adjacent side, use secθ."

Yu Chen hummed in agreement, then suddenly reached out and drew an extremely thin line on the back of his hand with a pencil—from the base of his fingers to his wrist bone, as if stitching up an unhealed wound.

“You have enough speed, but not enough power,” she said, her voice so low it sounded like she was reciting a code. “Teach for another ten days, and I’ll let you land a secθ-level critical hit with one punch.”

An Yi didn't pull his hand away; he simply turned his palm over so it was facing up and handed it to her—like handing a blank target to an archer.

"make a deal."

7:45 AM

The morning reading bell rang, and the two walked downstairs side by side. At the corner of the stairs, Gao Xuelan was holding a stack of test papers. Her gaze shot out from above her glasses, first landing on the pencil line on An Yi's hand, then sliding to the end of Yu Chenyan's red hair, and finally stopping at her right hand—the bandage had been washed off, and the bruise was exposed under the cold white light, like a cheap medal.

"Yu Chen," Gao Xuelan said, adjusting her glasses and speaking in a low voice, "come to the office after morning reading."

An Yi paused slightly, but Yu Chen reached out and gently pushed him from behind—like giving a boxer a "continue" gesture.

"Don't worry." Her voice was very soft, but loud enough for him to hear. "I will be self-disciplined, law-abiding, and will not fail you."

—

8:00 AM

The moment Zheng Baoguo stepped into the classroom, his first glance went to the last row—Yu Chen's seat.

The desk was empty except for a copy of "Required Course Four," its title page facing upwards, with a line of very faint words written in pencil:

“sin(α+β)=sinαcosβ+cosαsinβ

"I've learned it, thank you, teacher."

Below the handwriting, there was a drawing of an upside-down boxing glove, which looked like a surrender or a declaration of war.

Zheng Baoguo's age spot twitched slightly, but he ultimately didn't utter a sound.

He turned around and picked up the chalk to write the title of the new lesson on the blackboard—

"The tangent of the sum and difference of two angles".

The moment the chalk tip touched the blackboard, it made a crisp "click," like the second bell ringing.