My Unique Adaptation Skill in Another world-Chapter 57 - 56: Fuel for the long road.

The dining hall of the Arakami estate felt larger than usual that morning.

Not physically. The table was the same length, the chairs the same number, the morning light slanting through the same windows at the same angle. But one of the chairs was conspicuously, loudly empty, and that absence carried a presence strong enough to register like a sound that had suddenly stopped.

Akane noticed Leo noticing it.

"He left before sunrise," she said, reaching for the bread without looking up. "Private carriage to the Gate Hub. Didn’t tell anyone. His rooms were empty when Yuki went to check."

Leo looked at the empty chair. "How is Yuki?"

"Fine." Akane’s tone was carefully neutral. "She understands how he is. She always did." A brief pause followed. "She’s also somewhere between mortified and relieved, which is a complicated thing to be this early in the morning."

Iori sat at the head of the table with her tea, saying nothing. Her expression carried the quiet certainty of someone who had anticipated the outcome and was content to let it exist without commentary.

"He’ll probably be on the Third House ship already then?" Leo asked.

"Probably barricaded in his cabin even," Akane said. She pressed her lips together to contain a budding laughter, failed, and a short sound escaped her.

"Akane," Yuki said quietly from across the table.

"I’m not laughing, I swear." Akane replied.

She very clearly was.

Yuki looked down at her plate. The corner of her mouth shifted slightly despite everything.

Leo ate his breakfast and said nothing further about Takeshi. It was the most respectful option available and also the most accurate reading of the room. The humiliation had already happened. It would follow him home and do its work there. Adding weight to it here served no purpose.

When the meal ended, Iori set down her cup and looked at Leo directly.

"We have one stop before the delegation departs," she said. "The Imperial Palace, we need to go collect your actually prize."

---

The high-security wing of the Imperial Treasury was not a place that announced itself.

There was no grand architecture, no visible display of what it held. The entrance was a reinforced door set into the palace’s inner administrative quarter, guarded by soldiers whose armor carried no house insignia. Their expressions suggested they had been selected specifically for their ability to remain entirely unimpressed by anyone who arrived, regardless of status.

Iori’s credentials moved them through three checkpoints without difficulty.

The interior was pressurized differently from the rest of the palace. Leo felt it the moment the final door sealed behind them. There was a density in the air, not quite mana and not quite physical weight, but something that registered as both. The Treasury’s ambient enchantments, preservation layers, suppression fields, and anti-theft workings, built up over decades, had created an atmosphere that pressed gently against the senses.

A Treasury official met them inside. He was middle-aged and precise, carrying a ledger with the ease of someone who had cataloged extraordinary things for so long that they had become ordinary.

"The second-place medallion for the four-and-five star division," he said, confirming Leo’s credentials. "Grade-S vault access. Standard selection protocol. One item only. No modifications."

He led them through the outer chamber.

Leo had expected weapons. The chamber confirmed that expectation on a scale that took a moment to process. Blades of every design rested on velvet mounts beneath glass, some with visible enchantments glowing under preservation light. Staves, armor pieces, rings, and artifacts whose purposes were not immediately clear filled the space. Everything carried weight in the specific way of objects made with intent and preserved long enough to accumulate history.

He walked past them.

Not because they were not remarkable. They were. But he already had two swords, both made specifically for him by someone who had taken pride in their work. Adding a legendary blade would not solve his actual problem. His limitation was not his weapons. It was his ability to use them.

The official guided them through a second door.

This chamber was smaller, with fewer items, each given more space. The objects here looked less dramatic but felt heavier in presence, as if they did not need to announce themselves.

Leo stopped in front of a case near the far wall.

Inside, resting on dark velvet, was something that looked like a crystal but was not quite one. About the size of a closed fist, its structure was latticed rather than solid. Layered geometric formations caught the preservation light and held it instead of reflecting it.

It pulsed.

Not visibly. Not with the obvious rhythm of a heartbeat. But in a way that registered against Leo’s newly formed mana ring, like a sound just below the threshold of hearing.

The official appeared at his shoulder.

"The Primal Core," he said. "Recovered from a collapsed cultivation site approximately two hundred years ago. Its origin is unclear, possibly pre-Merge. It functions as a biological integration artifact. Extremely rare. Most candidates in this vault choose weapons since it’s proper use it up for debate."

"What does it do exactly?" Leo asked.

"It converts waste energy, the heat and kinetic friction generated by physical movement, into raw internal mana. The mana cannot be projected externally. It functions solely as an internal fuel source, we’ve tested with a golem and it mostly useless."

His tone remained flat, as though he were describing a kitchen tool.

"For most mages, it is also considered a poor choice. The mana it generates is too low-quality for spell work. But theoretically, for someone whose internal processes require significant energy to sustain, it would be considerably more useful. So the leading thought is that it could be helpful to people with special constitution, but the problem becomes how to properly integrate with it, but further research was scrapped."

Leo looked at it.

He understood the Adaptation Skill’s hunger from the inside. The caloric drain after heavy evolution. The exhaustion that followed the hunt, the zone. Every instance where his body had rebuilt itself under pressure and then demanded enormous fuel to sustain what it had become.

The starvation effect Axiom had identified. The problem that would only worsen as his adaptations became more complex.

A dedicated internal fuel source like this would solve a lot of his problem, especially considering how much activity he’ll be up to, so generating the energy won’t be a problem either.

"I’ll take it," he said.

The official opened the case, surprised that Leo had picked it, but wasn’t going to question his decision.

Leo reached in and picked up the Core.

The contact was immediate.

Not dramatic. No burst of light or sound. No theatrical reaction. Just immediate, like a door opening , one state replaced by another without transition.

The Core did not feel like crystal in his palm. It felt like something that had been waiting to be held by something alive and had finally found it, almost like it was made for him. The latticed structure began to warm. Not heat exactly, but something closer to the cool prickling of his mana ring, inverted and moving inward instead of across the surface.

His Adaptation Skill recognized it before he consciously processed what was happening.

Leo inhaled sharply.

The Core dissolved.

Not crumbled. Not broken. Dissolved. The lattice came apart in a sensation that moved through his palm, up his forearm, and into his chest, all without any visible change from the outside. He felt it settle. He felt exactly where it chose to reside.

His solar plexus.

The same general region as his aura core. The mana ring around his heart reacted too. The new core was distinct from both. It occupied its own space with the certainty of something that knew it belonged there.

Then came a weight.

Dense. Cold at first, the kind of cold that signaled integration rather than intrusion. And then, as he stood there with the Treasury official watching in confusion and Iori a few steps back with her arms crossed, the cold resolved into something steady.

A thrum.

It was different from his aura’s warmth and pressure. Different from his mana ring’s cool circulation. This was quieter than both and more constant, a background hum that required no explanation.

The Core was already working.

Already converting the heat from his metabolism into something stored and patient.

He exhaled.

"Interesting, that I can say has never happened before," the official said, making a note in his ledger. "Biological integration. This is the first recorded instance for this type of artifact. Usually it’s Weapons, and with external integration not internal."

"You are starting soon at the imperial academy correct?" His tone did not change.

Leo nodded.

"You will want to visit the Academy’s medical faculty within the first week, for documentation purposes."

Leo looked at Iori.

She was watching him with a familiar expression, one she wore when something exceeded her expectations.

"How does it feel?" she asked.

"Like I have a second heartbeat," he said. "But much quieter."

She studied him for a moment, then nodded once and turned toward the exit.