Three Years Old [Morning / Home]

Hajun was three years old.

His speech was slower than other children’s, and he could not walk for long.

But there were things he loved with certainty.

Yellow buses.

Strawberry milk.

And the sound of the door lock when his father came home.

Beep-beep.

Whenever he heard it, Hajun pushed himself up from the floor.

(Hajun) : “Daddy.”

Taekyung set down his bag and smiled.

(Taekyung) : “Daddy’s home.”

Hajun tottered toward him on his own.

One step.

Two.

On the third, his knees buckled.

Taekyung caught him quickly.

(Hajun) : “Again.”

(Taekyung) : “Again?”

Hajun nodded.

Taekyung sat a little farther away once more.

From the kitchen, Jian watched them, then turned her eyes to the calendar.

Rehabilitation.

Neurology.

EEG.

Developmental assessment.

Between the packed appointments, the number of days until Hajun’s fifth birthday kept shrinking.

[Afternoon / Laboratory]

At the very back of the culture room, inside an incubator, was an old sample.

HN-365.

Day 365 of culture.

A human brain organoid that had been growing for a full year.

Taekyung’s team had maintained it to study long-term culture and the possibility of vascularization.

It was smaller than a fingernail.

But inside it, immature neurons had formed layers, and some were already exchanging electrical signals.

Looking at the microscope display, Taekyung said,

(Taekyung) : “Check oxygen delivery to the core again.”

(Researcher) : “The vascular-like structures are better than last week.”

(Taekyung) : “Not just the structures. Check whether they actually function.”

The researcher nodded.

Taekyung always checked the same things.

Had it grown?

Was it alive?

Was it functioning normally?

Could it tolerate blood flow?

Could it potentially connect with surrounding tissue?

In organoid research, missing even one of those questions made the rest meaningless.

[Night / Home]

When Taekyung came home, the house was unnaturally quiet.

(Taekyung) : “Hajun?”

Jian’s urgent voice came from near the bathroom.

(Jian) : “Honey!”

Taekyung ran.

Hajun’s body was rigid in Jian’s arms.

His eyes were pulled to one side, and his arms and legs jerked in a steady rhythm.

Taekyung checked the time.

One minute.

Two.

Three.

The seizure did not stop.

It continued even in the ambulance.

Taekyung counted.

Six minutes forty seconds.

Seven minutes twelve seconds.

Eight minutes three seconds.

Only after medication was given in the emergency room did Hajun’s body finally relax.

[Dawn / Hospital Corridor]

Jian slid down against the wall.

(Jian) : “If it were his liver, I could give him part of mine. If it were a kidney, one of us could give him one.”

Taekyung could say nothing.

(Jian) : “Why did it have to be his brain?”

Her voice broke.

(Jian) : “I wish you could transplant a brain.”

Taekyung’s gaze stopped.

(Jian) : “If it were possible, I’d give him part of my own brain.”

For Jian, it was only a sentence born from despair.

But inside Taekyung’s mind, a different calculation began.

Hajun: three years old.

Time remaining: roughly two years.

The organoid in his lab: one year in culture.

Its developmental level was still far too immature.

For the first time, Taekyung realized the problem was not simply whether neural tissue existed.

It was whether that tissue could mature enough to be used in Hajun.