The unknown leather book he found inside the ruins where Dragapult was trapped!
In it, there is a more detailed illustration with numerous annotations and analyses, breaking down and examining the various components of a Pokémon.
Initially, when Natsuhiko saw the illustration, he thought it was the ancient people dissecting a Pokémon and experimenting on each of its parts.
But he didn't recognize that Pokémon.
However, when he saw Regidrago inside the Pulsating Furnace, he suddenly realized.
The drawings in that leather book were not some analysis experiments done after dissecting a Pokémon...
They were diagrams of Regidrago's body components!
The ancient people who once worked in that laboratory, their true purpose was never to study Pokémon, or rather, studying Pokémon wasn't their main goal. They wanted to continue what Regigigas couldn't finish!
They intended to create a body for Regidrago!
To let this formidable being, which had only a head yet wielded terrifying power, have a complete body, able to manifest its true form!
Because, on that diagram, the part concerning the head bore a striking resemblance to the Regidrago before them.
And they confined Dragapult, continually nourished it with energy to make it grow and become stronger, yet imparted no knowledge or taught it how to become an excellent and powerful Pokémon, providing nothing but energy to it, likely not for Dragapult itself.
What they needed was the abundant and pure Dragon Energy after Dragapult was fully grown!
Because the pure Dragon Crystal formed by Dragon Energy is extremely rare. Even Regigigas only found enough to create Regidrago's head from Dragon Crystal and couldn't fully make its body.
The ancient people couldn't find it either.
So they used a more straightforward, long-term, and enormously consuming method, yet one that could certainly satisfy the outcome.
They nurtured Dragon-type Pokémon to extract Dragon Energy!
Once Dragapult's pure heart was fully grown, they extracted its pure Dragon Energy to create Dragon Crystal and used it to fill Regidrago's body.
Back then, the laboratory probably raised more than just one Dragapult as Dragon-type Pokémon.
But because it is a Quasi-God Pokémon with a purer Dragon lineage, it was made the primary target of cultivation.
Those other stone chambers likely housed many Dragon-type Pokémon as well.
But due to some unknown reasons, the ancient people left, and the laboratory was abandoned.
In the end, only the long-lived Dragapult survived.
Perhaps when they were cultivating Dragapult, to ensure the Dragon Crystal formed in the future matched Regidrago's head, they did something to its energy.
Which is why it immediately sensed a summoning after being freed from its chains.
So to say.
Was Dragapult really designed by the ancient people to become part of Regidrago's body?
The thought occurred.
Natsuhiko could only feel one thing about these ancient people's ideas.
Madness!
To dare such thoughts about Regidrago, even at the cost of significant resources, forcibly strengthening Dragapult, the Quasi-God Pokémon.
Possibly counting in some other Dragon-type Pokémon as well.
The cost was enormous.
If they were truly successful, Regidrago's power and abilities would probably rival Regigigas', perhaps even surpass it, depending on whether the body they provided could perfectly match.
It's a pity all of this ended prematurely while it was still in the preparation stage.
Luckily Dragapult's mentality is still child-like.
Otherwise, if it realized it was merely a "tool" prepared by the ancient people for Regidrago, how would it feel inside?
From the looks of it, this Regidrago seems to be sealed within the Pulsating Furnace, unable to leave.
Regidrago and Dragapult's gazes met.
In the next second.
Thud!
Regidrago once more made a muffled sound inside the Pulsating Furnace.
Its eye lights flickered rapidly, causing the Dragon Energy within Dragapult to also stir.
Natsuhiko's expression changed.
Bang!!!
Suddenly, there erupted a fierce pulse of Dragon Energy from Dragapult, pushing Natsuhiko away.
"Yongji!"
Yujira used its psychic power to catch Natsuhiko who was thrown back.
Natsuhiko frowned, the impact didn't harm him, but Dragapult's state...
It was observed, the "Dragon Crystal" grasped in Dragapult's hand had somehow completely "melted" into a pure dark red Dragon Energy.
And Dragapult's eyes also lost their original luster, becoming somewhat dazed and confused.
Could it be under Regidrago's control?
That possibility wasn't out of reach.
If his guess was correct, Dragapult's Dragon Energy likely has a high compatibility with Regidrago's Dragon Energy!
This thought had just emerged in Natsuhiko's mind.
Thud!
The Pulsating Furnace again emitted a sound.
Dragapult, clutching that rich Dragon Energy, was about to throw it at the Pulsating Furnace.
It wants to break the seal!
Regidrago wants to use Dragapult and that remaining Dragon Crystal's power to break free of the seal keeping it within the Pulsating Furnace.
And the seal is likely the line engraved on the furnace, which flickers together with the magma.
The Pulsating Furnace combines the energy of magma, and if it successfully breaks the seal, this pulsating furnace will lose its ability to restrain the magma.
Then the magma will surge again, and the dormant volcano would instantly become active again.
This would inevitably put the Pokémon living around this volcano under terrifying magma attacks, with only a few possibly surviving, while most would certainly perish.
This volcano could even affect the entire Alternate Space.
But in the face of this situation, Natsuhiko found himself without a solution, whether against Dragapult or Regidrago, they were not within his power to contend with.
Unless...
Regigigas comes here.
"Dragapult!" All Natsuhiko could do was shout.
Bang!!!
Massive "waves" of magma surged, hot magma rushing toward his direction.
It was seen.
Dragapult, breathing heavily, grasped the Incubator in one hand and the pure Dragon Energy in the other, yet its hand was just about to land on the Pulsating Furnace, slowly rising from the magma.
Yujira's psychic abilities blocked the magma's erosion, and through a slight gap, it made eye contact with Dragapult.
The originally pure and clean eyes of Dragapult were now filled with too much.
Memories, thoughts, struggles, anger, self-mockery...
It lightly nodded to Natsuhiko and then, without hesitation, stuffed the pure Dragon Energy in its hand into the Incubator in the other hand.
It wanted to give all that energy to the Pokemon Egg of the Dragon-type Pokémon yet to hatch!
However, what puzzled Natsuhiko more was how Dragapult could break free from Regidrago's control.
Why, in just a fleeting moment, did it seem to have grown so much, both in mind and ability?
Those eyes absolutely weren't the same as the previous Dragapult.
In this bewilderment of his, Dragapult channeled the Dragon Energy, transformed from the Dragon Crystal, unreservedly into the Pokemon Egg.
In comparison to this Dragon Energy, the Dragon Scale Natsuhiko used previously seemed somewhat redundant.