Brain Domain Development!

After breakfast, wearing nothing but a pair of little underpants, Mercer lay on the operating table on the second floor of the Treehouse.

As his breathing followed Kureha's fingers pressing against him, he described the changes in his breathing and the subtle sensation of Qi coursing through his entire body.

He could sense a perception sweeping over him, as though it were penetrating his skin, flesh, and bones, observing the changes in his body as he breathed.

Kureha's expression was calm. She kept asking questions and occasionally jotting down notes. Being examined like this, as though he'd been stripped bare, made Mercer feel very uncomfortable.

He finally understood how it had felt when he'd used Observation Haki to scan Garp and Kureha.

It was so unpleasant!

After a long while, Kureha said calmly, "All right, that's enough for today. But we'll need to observe you over a long period."

"Still, you really are a treasure, kid. You quietly changed your breathing into a different method without anyone noticing. Fascinating, fascinating!"

She didn't press him for the reason behind the change. What mattered to Kureha was whether she could reproduce the result.

Mercer got up from the operating table, put on his clothes, and looked around.

The walls were white, and everything inside was arranged neatly. Some of the experimental equipment looked exceptionally precise.

Some experiments were still underway.

"Doctor Doriel, have you made any breakthroughs in your research on lineage factors?"

Mercer asked.

Kureha said, "Why?"

"Do you have any drugs for developing the brain? You've got things for strengthening the body, but what about the brain?"

A glimmer flashed in Kureha's eyes. She thought of the books Mercer had been reading lately, all filled with conclusions and theories about different aspects of the human body.

"Brain development is a very mysterious field of study. Why are you thinking about it?"

Kureha asked.

Mercer thought for a moment. "After reading those books, I've been thinking about it a lot lately. The human brain can generally only be developed to around 10 percent at most, while ordinary people usually reach only about 3 to 5 percent.

"And that encyclopedia said that users of the Brain-Brain Fruit throughout history were generally able to develop their brains to around 20 percent. They could do amazing things like never forgetting anything they'd seen and learning a new language in an hour.

"The books also included some theories that once the brain develops to a certain degree, or reaches a particular point, a living creature might gain extraordinary abilities—abilities no less remarkable than those of Devil Fruit users."

"And the physicist William Gallon also said, 'Anything humanity can imagine might become reality.'"

There had been many theories about brain development in his original world, too. Now that Mercer had read those books, he'd made up his mind.

"I want to try developing the brain's potential. I want to see whether increasing brain development could be a unique path of biological evolution. I want to see what a living creature becomes when its brain reaches 100 percent."

The smartest person in his original world, Einstein, was said to have developed no more than about 15 percent of his brain.

His original world was ordinary, with no extraordinary powers to be found. But in this world, with its many mysterious powers and resources, Mercer didn't think his ideas were mere wishful thinking.

Kureha narrowed her eyes. She had always studied the human body and Longevity Medicine. Now, at nearly 121 years old, she was still in peak condition, with many years of life ahead of her.

As for the brain, Kureha said calmly, "It's an interesting idea. The human brain makes up only 2 percent of body weight, but it consumes about 25 percent of the body's oxygen and 17 percent of its energy. The brain is a mysterious, unexplored field."

The human brain contained roughly 14 to 16 billion neurons, with hundreds of billions of connections between them—more than the stars in the known universe.

You didn't think much of it until you did, and then it was astounding. Mercer's ideas had certainly opened Kureha's eyes. She was a doctor, and while she might not be the best researcher of the human body in the world, she was at least among the top three.

Kureha knew of several ways to extend one's life, and she was still trying them. But she had reached a bottleneck without even realizing it. Should she try an entirely new path?

And so—

"Kid, developing the brain isn't some simple physical experiment. The slightest mistake could turn you into an idiot. And modern medicine isn't equipped to deal with that kind of thing. Have you thought this through?"

Kureha asked seriously.

Kureha had never thought of little Mercer as an ordinary kid. After all, most children his age were either playing in the dirt or eating and sleeping all day.

Mercer grinned. "Isn't that why I have you, Doctor Doriel? I'm not skilled enough yet, but that doesn't mean you aren't. You're still young, and I'm still little. We have plenty of time to study it."

Kureha froze at his words, then gave a helpless, exasperated laugh. She scolded him, "You little brat, dreaming big, aren't you? You're already trying to boss me around before we've even started. I haven't even said whether I agree."

Mercer's little face grew serious, and he looked a little nervous. "Then, Doctor Doriel, will you—?"

Seeing this, Kureha narrowed her eyes, looking amused. "I could agree, but you need to understand that research doesn't start just because you flap your lips. You need funding, equipment, and materials. You can't do without any of them.

"Do you have millions of Beli? Do you have state-of-the-art equipment? Do you have all sorts of experimental materials related to the brain? Brain development requires materials, to say nothing of rare and precious herbs and the brains of various creatures—large beasts and Sea Beasts, for example. You need strength to get those. Do you have it?"

Kureha laid the harshest realities right in front of Mercer.

If these problems weren't solved, research into brain development would remain empty talk. Even if he could still study it, progress would be painfully slow.

She wasn't trying to dampen Mercer's enthusiasm. These were obstacles they couldn't avoid. There was one more thing Kureha hadn't mentioned.

Even if Mercer managed to gather everything they needed, research into the unknown could still fail.

Watching Kureha's imposing Aura, Mercer smiled. A hint of defiance flickered across his little face.

He answered calmly, "I'm not even three years old, and I can already beat thirteen grown adults. I'll definitely be very, very strong in the future. I'll earn the money myself. Bear Cub has the Munch-Munch Fruit, so I think it can combine the equipment we need. As for the experimental materials, they won't be a problem once I'm grown."

For a moment, Kureha stared at Mercer, a little dazed. There seemed to be a unique quality about the kid that made people believe in him.

"I must be crazy. I've actually been persuaded by a kid."

Kureha couldn't stop the corners of her mouth from lifting. She let out a delighted "Hehehe!"

"Then I'll agree for now. If you can't do it someday, I'll pull down your pants and spank your bottom raw."

Mercer's face suddenly stiffened. He swallowed and looked thoroughly dejected. "By then I'll be grown up. Would you really be okay with pulling down my pants?"

Kureha looked down at Mercer and said calmly, "I raised you from the time you were covered in shit and piss. I've already seen everything there is to see, whether I should or not. I don't care, so what do you care?"

"Crude," Mercer muttered.

Kureha glanced at him and said calmly, "Say that again?"

"No, I didn't say anything."

Mercer had nothing else to do here, so he went downstairs and took Bear Cub, who was starving, out to his vegetable garden.

Purple Bamboo Forest.

Two more days passed.

At nine o'clock that morning.

Kureha got ready to leave. She spoke to Mercer, who was reading at the desk:

"I'm going to the Royal Castle on Drum Mountain to collect the medical fees from a few days ago. Stay home."

Mercer turned to look at her. "Will you be all right going alone? Your fees are always outrageous. What if the king has bad intentions?"

Kureha raised an eyebrow and smiled calmly.

"In this country, I can go wherever I want. The old king won't do anything to me."

Watching Kureha's confidence, Mercer said, "Then be careful. But take your weapon with you. That's several million Beli. You don't want anyone stealing it."

"Do I look like a weakling to you?" Kureha teased. "Bet you I could make you call me Mommy with one hand."

Mercer looked at Kureha and suddenly said very seriously, "Doctor Doriel~ Mommy, have a safe trip!"

The corners of Kureha's mouth twitched violently. She laughed in exasperation. "You little rascal, don't call me that. I'm not your mother. Call me Doctor Doriel."

Still laughing, she walked out with a spring in her step. Mercer used Observation Haki to sense Kureha walking away, then got up, put on his "Laboon" coat, and picked up his weapon.

He left a note for Kureha.

Bear Cub, who had been waiting at the door for ages, gave a little "Ying," pushed the door open with a paw, and darted outside first.

With a bamboo basket on his back, Mercer closed the door.

He put the key in its usual place.

The snow crunched beneath their feet. As sparse snowflakes fell, a person and a bear vanished into the Deep Forest.

Pandas had very poor eyesight, but their senses of smell and hearing were exceptionally sharp.

Bear Cub had been exposed to Herbs since it was only a few weeks old. Being around them so much had given him a talent for finding rare medicinal plants.

Bear Cub was clever. Along the way, his keen sense of smell and hearing helped him detect dangerous creatures' territories, which he never approached.

Their motto was simple: sneak into the mountains quietly and make a fortune without a sound.

Mercer was happy to let Bear Cub lead the way.

They wandered through the snowy forest deep in the mountains, discovering one medicinal plant after another. When they found a suitable one, Mercer harvested it with practiced skill.

If they came across something they could eat on the spot, he let Bear Cub have a taste. Drum Island was small, but it was by no means lacking in resources. They came across all kinds of creatures along the way.

Their goal today was to gather herbs.

They weren't doing anything else.

If some creature foolishly got in their way, they'd just have to feed it to Bear Cub. With the Munch-Munch Fruit's ability, Bear Cub wasn't the same bear as before. He could eat anything, no matter how raw or cold.

The herbs they gathered came in many varieties, some from trees and others from grasses.

Bear Cub also got to fill his belly on tree-based herbs they couldn't use, and the same went for the grass-based ones.

Mercer was now a fully qualified herb-gatherer, and Bear Cub was undoubtedly a fully qualified "trash can."

The best thing about a Munch-Munch Fruit user was that nothing could upset their stomach.

They occasionally ran into others gathering herbs or hunting in the mountains, but everyone avoided each other well in advance. They stuck to their own business.

Around five in the afternoon, Mercer and Bear Cub began their journey home. At one point, a rustling came from some bushes not far ahead.

Mercer took the basket off his back.

He gripped the Axe Handle tightly and swept the area with Observation Haki. A snow-white Laboon burst out.

It looked like a rabbit, had the build of a bear, and charged toward them on all fours at high speed.

It was about a meter and a half long.

Mercer narrowed his eyes.

"There aren't any other auras around. It's alone—or still young."

A second before the Laboon reached him, Mercer turned aside and stepped back with his right foot. He could see its gaping mouth and sharp fangs. At the same time, he swung the axe in his right hand diagonally across it.

Squelch!

Using its forward momentum, he cut through its neck with the blade, severing its windpipe. A spray of crimson blood burst out.

Mercer moved past the Laboon, lowered his axe, and flicked the blood off the blade.

It was a very cool pose.

Mercer turned around, beaming, and looked at the Laboon twitching all over in the snow. It was clearly beyond saving.

A few seconds later.

A grain-sized, irregular crystal with a mysterious sheen appeared.

[Obtained F+-rank Soul Crystal ×1]

Mercer had obtained two Soul Crystals in total so far, each about the size of a grain of rice.

Small animals like rabbits, or creatures below F-rank, couldn't be refined into Soul Crystals after being killed.

The same went for small fish and shrimp.

An ordinary human child, for instance, wouldn't reach the minimum F-rank strength, either.

The appearance of a Soul Crystal meant the Laboon had died.

Mercer went closer and examined it carefully. Its fur was glossy and pure white—a fine pelt for making clothes.

He took a Surgical Knife from the inner pocket of his Laboon fur coat and began cutting along the Laboon's midline.

Medicine was divided into many complicated fields, including surgical anatomy.

Kureha was an absolute master of medicine, not only in her own skills but also in teaching.

Thanks to his A-rank Gift, [Breathing], Mercer had become much better at controlling his body. His mind was calm, and his fingers were nimble.

He used professional techniques.

Without damaging the Laboon pelt's grain, Mercer removed it in one complete piece.

He gutted the carcass, cleaned out the entrails, and washed them with the snow nearby. He tossed the clean entrails to Bear Cub for a snack.

He chopped off a few branches to make a sled and piled the prepared meat onto it.

Bear Cub had eaten plenty of household supplies these past few days, including ropes and harnesses. Now, a rope appeared and connected Bear Cub to the makeshift sled.

A bear pulled the sled.

Half an hour later, at a well-regarded tailor's shop in Keister Town, Drum Island's skiing destination, Mercer came to an agreement with the shop owner.

In exchange for half of the valuable Laboon meat, the tailor would make the Laboon pelt Mercer had brought into a fur coat.

He would come back in a month to pick it up.

He took the receipt.

Sitting on the sled, Bear Cub strode out of town on all fours. By the time the sky began to darken, Mercer had finally reached home.

The Treehouse was brightly lit. Kureha had evidently returned, too.

He opened the door, brought in the herbs and the remaining half of the Laboon meat, and put everything away.

There was a sizzling sound from the kitchen. Kureha was cooking. Hearing him, she called out, "You little brat, didn't I tell you to stay home today?"

"I went to gather herbs, and took Bear Cub out for a snack," Mercer replied with a grin. "Doctor Doriel, I was lucky today. I caught a Laboon!"

The next second—

Kureha came out with a spatula in her hand, her face dark.

"A Laboon?"

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PS: Soul Crystal sizes by rank:

F: Grain of rice.

E: Soybean.

D: Broad bean.

C: Pigeon's egg.

B: Chicken egg.

A: Goose egg.

EX Demigod: Human head.