Central Sabnock Plains.
The place that had once served as the territory of the magic beast Sabnock — from which the plains derived its name — was a point known as a "dragon vein," where subterranean flows of mana burst forth to the surface.
Around dragon veins, plants grew easily and powerful monsters were born in abundance.
Moreover, cities built atop dragon veins were said to prosper since ancient times, and wars had even been fought over the right to claim them.
Rest and his companions had been cutting down monsters as they advanced across the plains, and had nearly reached the central region.
"Now that I think about it… it's a strange thing, isn't it? I can understand monsters growing stronger after absorbing mana, but why would a city prosper? Does the mana from a dragon vein have the power to strengthen even a town?"
The one raising these questions was a party member investigating the central plains alongside Rest.
She was Yuri Cattleya, daughter of the knight commander.
Yuri had until recently been… not confined, but placed under the protection of the Cattleya marquisate's estate. She had run away once again, however, and made her way to the royal capital.
From there, she had volunteered to join Rest in the frontier development effort.
"If monsters grow stronger from it, maybe humans do too? If strong people are living in a city, I can see how it would prosper!"
"That's… not exactly a simple problem. Also, your voice is way too loud."
"Hmm… did you say something, Lord Lubeth?"
"I-I didn't say anything! D-Don't come any closer, you overdeveloped—"
"There's no need to run away. Come now, come now."
Wilhelm Lubeth, a fellow party member, leaned his body back in the same manner as always.
He still seemed to be no good around women — the moment Yuri closed in on him, he leapt backward at twice his usual speed.
Six humans were gathered at this spot.
Every one of them was a combatant worthy of being entrusted with investigating the heart of the demon realm.
First was the investigation team's leader, Rest Clover.
He held the title of count and was the very person who had subjugated the magic beast Sabnock.
Though young in age, he was a young man who possessed both the name and the ability to lead the expedition.
Next was Wilhelm Lubeth.
A comrade-in-arms who had fought alongside Rest against Sabnock.
Despite being a first-year student, he already possessed swordsmanship on par with — or exceeding — that of an active-duty Royal Guard. He was known as the "man-hating Sword Saint."
And then… a familiar friend of Rest's: Yuri Cattleya.
Though she had joined the development corps on short notice, Yuri had cut down a great number of enemies during the recent civil unrest.
In terms of physical ability alone, she was at the top among this group — a fighter powerful enough to slaughter monsters with her bare hands, even without a weapon.
"Hey, you two, quiet down! If you make too much noise, monsters will be drawn to us!"
The one who hushed them in a low voice was Isis Carbelt.
She was the leader of the student council enforcement division, and had earned a baroncy for the feat of rescuing numerous students during the stampede at the Magic Hunt Festival.
Isis was likewise a top-class fighter at the Royal Academy. Had she not been ennobled as a baron, she would undoubtedly have joined the Royal Guard — such was her extraordinary caliber.
"…………"
"My, my… This is like a school field trip. What a handful."
And then… two companions who were meeting Rest for the first time.
The man silently trailing at the rear was a priest in clerical robes, carrying a mace and possessed of a surprisingly sturdy build for a clergyman.
His name was supposedly Jax Rail. He had been dispatched from the temple as reinforcement and served as the party's medical staff.
Then there was a knight sent from the royal palace: Oliver Argil, who for some reason wore an unpleasant expression on his face.
Like Rail, he was a reinforcement recruit, yet he was burning with unusual motivation for this particular mission and watched the lighthearted exchange between Yuri and Lubeth with a stern gaze.
"And here I have my career as a knight riding on this… Honestly, could you two take this a little more seriously?"
Argil muttered to himself while nervously tapping the hilt of his sword with his finger.
According to the information they had been given beforehand… Argil was a distant relative of the queen dowager's faction.
As the third son unable to inherit the family headship, he had been pushed out of his household and joined the knight corps. From there, he had steadily risen through the ranks on the strength of his abilities.
Had things continued smoothly, he could have reached a respectable position within the corps — but because his relatives had taken part in the civil unrest, he had been swept aside and derailed from the path of advancement.
For that reason, he was desperate to clear his name by ensuring the success of this mission, and his irritation at the team's lack of seriousness was plain to see.
(Well, I can understand his position. His abilities are apparently well-proven, so as long as he doesn't cause trouble…)
The reason Argil and Rail had been added to the investigation team was Andrew's consideration — he recognized that sending students alone on such a dangerous mission would be irresponsible.
It was obvious that Rest and Lubeth possessed considerable combat ability, but their youth still meant a lack of experience.
To compensate for those shortcomings, seasoned knights and priests had been assigned to accompany them.
"Yuri, Lubeth. Miss Isis is right. Let's maintain a bit more tension."
As the team's leader, Rest admonished the two.
"Ah, sorry. I guess I got a little carried away."
"…Hmph. My bad."
Yuri apologized sincerely, and Lubeth, snorting through his nose, offered a half-hearted apology of his own.
He glanced toward Argil… and seeing that the reprimand had apparently satisfied him somewhat, the knight settled into a stern silence.
"In any case… to answer Yuri's question, the dragon vein doesn't directly make a city prosper. The mana that erupts from it can be used to erect barriers that ward off monster incursions, natural disasters, and plagues. That's why cities built on them prosper in the end."
"Oh, I see… As expected of you, Rest. That makes sense."
Drawing on the knowledge from the books he had read at the House Rosemary estate, Rest explained. Yuri folded her arms and nodded with an impressed expression.
A barrier that suppressed natural disasters and monsters, combined with surrounding land where crops grew more easily — it was no wonder such cities thrived.
And of course, once it was understood that a city would prosper there, wars to seize it were only natural.
"More importantly… it should be around here. This is where I fought Sabnock."
They had arrived at precisely that spot.
Before them lay a hole gouged by "Amaterasu," and traces of destruction could be seen everywhere.
"So this is… it…"
"Mm…"
"…………"
Everyone except Rest and Lubeth held their breath.
The remnants of battle left at this site were so fierce that they seemed impossible for a human to have wrought.
Once again, the scene made it clear that the battle between Rest and Sabnock had been something beyond all common sense.
"The center of the plains lies just ahead. There will be strong monsters lurking there, so… everyone, be on your guard."
"…………"
Leading his now-unnervingly quiet companions, Rest pressed deeper into the plains.
"Now, from here on, we enter the center of the plains — the deep layer of the demon realm. Everyone, please be extremely careful."
With that call to his companions, Rest set foot for the first time into the deepest reaches of the demon realm.