D-DAY [D-641 / Laboratory]

Taekyung conducted two different kinds of research by day and by night.

During the day, he was the Taekyung everyone knew.

He reviewed his researchers’ data and cut down any interpretation that went too far.

(Taekyung) : “Being alive and functioning normally are not the same thing.”

When the meeting ended, the researchers left one by one.

And after the last door closed,

Taekyung went back into the culture room.

That was when the research no one knew about began.

He never uploaded it to the shared server.

He never wrote down its real purpose.

He quietly kept small amounts of cultures that had been scheduled for disposal during the day and checked them alone each night.

At first, the neural circuits were the problem.

The accelerated tissue looked mature on the surface, but its signals were chaotic.

Some regions were excessively excitable.

Others barely responded.

Taekyung slowed development again.

He waited until the necessary cells caught up, then accelerated once more.

D-603.

This time the circuits stabilized.

Then the blood supply failed to keep pace.

The larger the tissue grew, the more cells died at its core.

Taekyung changed the conditions again.

He created pathways for oxygen and nutrients before pushing the neurons forward.

D-548.

The necrosis stopped.

Next came tumor risk.

Some rapidly dividing cells would not stop proliferating.

Taekyung discarded the entire batch.

A month vanished.

He began again.

D-497.

This time proliferation stopped at the target stage.

Then came survival after transplantation.

Then integration with the existing brain.

Then the question of whether the tissue could continue developing alongside a growing child’s brain.

Every solved problem revealed another behind it.

Taekyung slept less.

Three hours.

Two.

Some nights, he never went home.

Jian did not know exactly what he was researching.

The people in his lab knew even less.

They only thought Professor Taekyung had become even more demanding than before.

No one knew what he checked alone every night,

or why certain cultures vanished from the disposal list.

[D-412 / Animal Laboratory]

Taekyung carefully compared data obtained within the approved scope of his existing research

with the data he had generated in secret.

The transplanted tissue survived.

Host blood vessels entered it.

A few days later,

a signal that began in the host tissue passed into the transplant.

Taekyung froze the screen.

He stimulated it again.

The same response.

He reversed the direction.

This time, a signal originating in the transplanted tissue passed into the host network.

Bidirectional.

Taekyung stared at the monitor for a long time.

His fingertips trembled.

Even then, he did not celebrate.

A new question had already appeared.

‘How long does it last?’

D-356.

Long-term survival.

D-301.

No abnormal hyperexcitability.

D-263.

Connection maintained in a developing brain.

D-219.

Return to normal developmental speed after accelerated conditions were removed.

One by one, he passed them.

The numbers in his notebook continued to fall.

It was the period in which Taekyung made more discoveries than at any other point in his career.

And at the same time,

the period in which he hid the most.

[Afternoon / Research Ethics Review Board]

Taekyung tried one last time to choose the proper path.

His son’s name appeared nowhere in the application.

Potential use of accelerated neural tissue in pediatric brain disease.

Preclinical data.

Expected risks.

Possible benefits.

He organized everything he had and requested a formal review.

One of the reviewers asked,

(Reviewer) : “Professor, if you were sitting on this side of the table rather than applying, would you approve this?”

Taekyung fell silent.

He already knew the answer.

(Taekyung) : “No.”

(Reviewer) : “Then why submit it?”

Taekyung answered slowly.

(Taekyung) : “I wanted to know whether it was at least worth considering.”

A few days later, the decision arrived.

‘Human application denied.’

Insufficient evidence.

Unknown long-term risk.

Excessive ethical risk in pediatric application.

Taekyung read the decision from beginning to end.

There was not a single sentence he could call wrong.

If he had been reviewing it,

he would have rejected it too.

That night, Taekyung remained alone in the lab.

He placed the rejection notice inside a drawer.

Then he took out a separate notebook.

Its first page had begun long ago.

D-730.

Hundreds of pages followed.

D-603.

D-412.

D-219.

Taekyung opened to the latest page.

D-37.

Thirty-seven days remained.

Beneath the number were the barriers already passed.

Developmental stage.

Normal neural circuits.

Vascularization.

Long-term survival.

Tumor risk.

Functional integration with existing brain tissue.

Continued development alongside the growing brain.

Taekyung stared at the last empty line.

‘Human.’

There was no way to test that one beforehand.

And that was the greatest barrier of all.