Set and the Water Wolf were clearly sensing something, but Rei couldn't tell at all what was happening at the end of their gaze.
Even so, judging from their behavior, it was obvious they weren't doing this as a joke. There was unmistakably some real reason behind it.
Moreover, what Set and the Water Wolf were both focused on was the center of the Treant Forest.
And in that center lay a vast Underground Space—home to the Wisp.
The Wisp, which possessed the ability to summon both living and non-living things from another world.
Given the circumstances, Rei was certain something had happened to the Wisp.
(The question is what caused it... Anastasia, or Grimm?)
Anastasia, who was researching the Wisp in the Underground Space, likely didn't know, but that space was connected to Grimm's laboratory.
That being the case, the possibility that something had occurred during Grimm's research of the Wisp couldn't be denied.
In this situation, it was difficult to make that judgment from the outside.
Grimm and Anastasia.
Which of the two had caused this incident—he needed to go see for himself.
Even setting that aside, Rei harbored hopes for the Wisp—that perhaps it could take him to Earth even just once.
Considering that something had happened where the Wisp was, he couldn't just sit here doing nothing.
What had happened?
He needed to find out.
"Set!"
"Gruu!"
Set responded instantly to Rei's shout, coming to his side in a heartbeat.
Rei mounted Set's back, but before heading to the Underground Space, he called out to the knight in charge here.
"I'm going to check on the situation. It's probably fine, but prepare yourselves to handle whatever comes up."
"Understood. Be careful out there."
Rei nodded at the knight's words and was about to head toward the center of the Treant Forest with Set when—
"Wan!"
—the Water Wolf called out to stop him.
For the Water Wolf, the lake that served as its current home sat right next to the Treant Forest. Given that, it was only natural for it to want to deal with whatever was happening there.
Rei understood that, but he shook his head at the Water Wolf.
"Sorry, but wait here. As long as we don't know what exactly happened over there, I can't bring you along."
Since he truly had no idea what was happening on the other side, there was no telling what might happen to the Water Wolf, which was connected to the lake through water.
That being the case, he couldn't bring along a creature that was friendly to the people of this world.
...If this were still a situation where they only had to deal with easy opponents like the Goblin settlement, it might have been a different story.
"Please."
"...Wau..."
The Water Wolf accepted his words, albeit reluctantly.
It was also curious about what was happening at the center of the Treant Forest, but a major reason for its compliance was the concern that if it died or vanished for some reason, there was no telling what would become of the lake.
"Then I'm leaving this place to you. For now... if I haven't returned by tomorrow morning, seek instructions from Lord Daskar. If you tell him I went 'underground,' he should understand."
Rei understood that the existence of the Underground Space needed to be kept as secret as possible. That was precisely why he didn't mention going to the center of the Treant Forest, and instead left a message to seek instructions from Daskar.
If told that Rei went "underground," Daskar would naturally understand that he had headed for the center of the Treant Forest, and would be able to issue orders if something happened.
(I would have preferred to keep "underground" a secret too, but that can't be helped.)
Between the Underground Space and the center of the Treant Forest—if asked which to keep secret, it was unquestionably better to conceal the fact that the Underground Space existed there.
Having left his message, Rei signaled Set and broke into a run.
"Run on the ground."
"Gruu?"
At Rei's words, Set let out a questioning purr, as if asking, "Are you sure?"
Set knew Rei was in a hurry, which was exactly why he thought it would be better to fly.
In fact, the speed at which Set ran, weaving through the trees of the Treant Forest, was already quite fast. Even so, it was an undeniable fact that flying would be faster.
But having just hidden their destination, taking to the sky would reveal where they were headed. While no one would know the exact direction or distance, considering the matter of the Wisp, Rei naturally wanted to keep things as secret as possible.
"Yeah."
To Set's questioning look, Rei nodded readily. Seeing that, Set started running along the ground without any further objection, trusting Rei's judgment.
However, his speed was overwhelmingly faster than when he had carried Anastasia.
Set also instinctively understood that the current situation was no ordinary matter. Given that, there was no reason to hesitate in rushing to the place where something had gone wrong.
As the scenery streamed past, Rei stroked Set's back.
(If something happened in the Underground Space where the Wisp is, the problem is that Set can't fit inside.)
The passage leading to the Underground Space was quite narrow. People like Rei, Anastasia, and Fana could pass through without issue, but only single file. Since two people couldn't walk side by side, even Set with his Size Change skill would have difficulty getting down there.
(Which means I really do need to head to the Underground Space alone this time. No—if Grimm is there, maybe he could identify the cause of the anomaly...?)
Even as Rei harbored that faint hope, Set ran along the ground toward the Underground Space where the Wisp awaited.
To arrive even a little faster.
Rei spotted a few Goblins along the way, but while he might have dealt with them before the anomaly, in the current situation, he had no time to spare for Goblins.
Without so much as striking them in passing, he advanced forward, truly ignoring them completely.
Set understood the situation as well... no, precisely speaking, since it was Set who had sensed the anomaly alongside the Water Wolf, it would have been stranger if he didn't feel even more urgency than Rei.
That being the case, Set likewise paid the Goblins no heed whatsoever as he dashed through the Treant Forest.
The Goblins, for their part, had no means to attack the swiftly moving Set. Even if they had some kind of weapon, Set would blow past them before they could strike.
Even Goblins with bows couldn't manage a shot—by the time they spotted Set, it had already left the area. And even if by some chance they could attack, Set was running through dense forest where many trees grew, making it all but impossible to land a hit.
Simply put, it wasn't an attack the average Goblin could pull off.
And so Rei and Set had absolutely nothing to do with the Goblins... though the ones that unfortunately leapt out in front of Set were sent flying, crashing into trees with enough force to shatter their bones or snap their necks, killing them on the spot.
Pressing onward through all of this, Rei and Set eventually arrived at the entrance to the Underground Passage leading to the Underground Space.
"This is..."
He hadn't been able to tell anything from the campsite, but at this close range, Rei could finally understand what Set and the Water Wolf had reacted to.
Rei didn't possess the ability to sense ordinary magical power. But even he could feel the abnormal atmosphere once he'd come this far.
It wasn't magical power, nor bloodlust, nor hostility... he couldn't put it into words, but it was an unmistakably alien sensation.
"A first-time sensation, huh. The fact that I'm feeling it from here means it's probably related to the Wisp, but... Set, I'm going inside. I need you to scout the perimeter. Given the current situation, I doubt anyone will recklessly approach, but there's always the chance."
"Gruu? ...Grururuu..."
Normally, Set would obey Rei's words without question. But sending Rei into the Underground Space under these circumstances felt extremely dangerous, even from Set's perspective. It couldn't bring itself to nod so readily.
Rei stroked the head of the worried Set.
"Don't worry. I don't know what's going on down there, but do you really think it'd be enough to do me in? You know my strength better than anyone, Set. We've been through everything together."
"Gruu..."
Set purred, looking reluctant. If asked whether he truly doubted Rei's abilities, he could say with certainty that no one knew Rei's strength better than he did.
"See? So trust me and wait here."
"Grururuu... Gruu."
Eventually, reluctantly—truly reluctantly—Set nodded.
After giving Set's head one final pat, Rei headed for the Underground Passage.
"Whoa... what is this?"
He didn't sense any particular danger, but there was definitely something strange. Puzzled by it, Rei pressed on through the passage until he reached the Underground Space where the Wisp resided.
"..."
Standing before that space, Rei fell silent.
No—to be precise, even if he had tried to speak, no words would come. That was the truth.
When he had visited this Underground Space that morning, the scene had been the same as the night before. The giant Wisp hung in the air, and off to one side sat a table covered with research documents, experimental apparatus, and preserved foods—dried fruits, hard-baked bread, and Dried Meat.
Also, though only Rei could tell, various Magic Items Grimm had placed were positioned throughout the space.
But now, none of that remained before his eyes.
The Wisp was still there, yes, but the table and everything on it was gone. In its place—though whether it was truly a replacement was debatable—a massive hole, roughly three meters in radius, had torn open in the very fabric of the space.
On the other side stretched a grassland utterly unlike this Underground Space.
Rei's eyes were riveted by the unexpected sight, but he immediately called out the names of the two who should have been there.
"Anastasia! Fana! Are you here!?"
He shouted, but as expected, no answer came.
If Anastasia were still here, it wouldn't have been strange for her to be examining the hole that had opened in space, fascinated by the unknown phenomenon.
(No, wait... could they have taken an interest in the spatial hole and gone through to the other side?)
Whether passing through the hole would safely deliver someone to the other side, Rei didn't know. But the scent of grass and soil drifting through from the other end suggested that, in all likelihood, the hole was passable.
The real question, though, was whether whoever went through could come back.
『Rei.』
A voice suddenly reached his ears—one he recognized.
"Grimm?"
『Yes. ...It seems an unexpected situation has occurred.』
Saying that, Grimm appeared.
Since his head was a skull, his expression was unreadable, but even so, a hint of trouble leaked through the edges of his words.
"Do you know what happened?"
『No, I avoid appearing here during the daytime as much as possible. However... the fact that the two who were here are now absent means...』
Grimm's eyeless gaze turned toward the hole in space.
What Grimm was implying, Rei understood immediately.
Whether Anastasia had gone through of her own accord, or been caught up when the hole opened—he couldn't say.
"Likely they went to the other side, huh. In that case... what should I do? Notify Lord Daskar... no, that won't work. Having more people gather here would only make things worse. Which means... me."
So Rei muttered, but in truth, his curiosity was already burning at the prospect of potentially reaching another world. There might be unknown Magic Items on the other side.
Harboring such thoughts—
"All right. I'll go take a quick look."
—he declared.