Why is my Isekai in the Slice of Life anime was become a Horror Story?

Chapter 9: Another Set of Rules, Those Who Act on the Other Side

[Rules of Conduct for Personnel Exploring the Isolation Zone:]

[Welcome to the Cave Research Base. Your dedication and effort will form the foundation of progress for the entire United States.]

[As an isolation zone exploration personnel participating in this experiment, you are required to comply with the following rules of conduct. Only after completing three exploration missions without errors will your criminal record be expunged. For your future, make reasonable choices.]

[The rules are as follows:]

1. Each clause in these regulations is critical. Violating these rules will result in various punishments depending on the severity, including detention for 3-7 days, food deprivation for 1-3 days, the addition of one exploration mission, or execution.

2. You must wear the designated yellow-striped uniform throughout the exploration. Damaging the uniform is considered a severe violation.

3. You must carry all exploration equipment, including the uniform, live recording device, thermal sensors, specialized sensors, environmental analyzers, lighting equipment, and headset. Before departure, ensure all equipment is in working order. If equipment malfunctions during exploration, it will be treated as a severe violation.

4. Instructions from the command room take precedence over these regulations. If the regulations conflict with the command room's instructions, follow the instructions. Disobeying the command room's orders is an extremely severe violation.

5. A standard exploration team consists of three members. The team leader must check the number of team members every 15 minutes to ensure it remains three. If a member is missing, exploration must cease immediately. If extra members are discovered, report this to the command room and follow their instructions. Do not interact with surplus explorers.

6. The target exploration zone contains hallucinogenic gases. Inhalation is not life-threatening but will cause harmless hallucinations. Do not overreact to visual or auditory hallucinations during exploration.

7. Upon returning from the cave area to the isolation zone, you must undergo approximately three hours of examination. During this period, follow the instructions of examination personnel. Violation of rules allows examiners to execute you directly.

8. If your uniform is severely damaged during exploration, you may change into another outfit. Various outfits, such as casual wear, staff uniforms, and firefighter gear, are available in the cave. Outfit changes will follow instructions from the command room. Do not mix outfits associated with different identities.

9. Destroying research equipment is an extremely severe violation, especially damaging headsets. Ensure you follow the command room's orders. Your actions must always comply with instructions.

10. If your communication device is severely damaged and unable to receive instructions from the command room, tear the side of these regulations. Beneath the standard rules, there is an emergency guide you can use to return to the base safely.

[These are the basic rules you must follow during the exploration process. Other rules will be issued per the command room's instructions.]

[By signing the contract to participate in this experiment with the research base, you have become someone contributing to the future of humanity. By adhering to the rules of conduct and completing the specified number of exploration missions, your criminal record will be completely erased. Seize this unique opportunity.]

....

The document was not overly lengthy, about a thousand words.

Kaguya finished reading in a short time and tried crumpling the sheet slightly. She quickly realized that the document, which appeared to be a single sheet, actually concealed another page inside. If torn, another document would undoubtedly be revealed.

Kaguya was slightly curious about what the hidden document might contain.

However, she couldn't act recklessly at the moment. Through her headset, she heard a cold, raspy voice, as if something was stuck in the speaker's throat, ordering her to enter the cave.

For now, she had no choice but to follow the directive.

Kaguya took the lead, stepping toward the dark tunnel behind the isolation door.

The surveillance camera at the entrance slowly tracked Kaguya's footsteps, its blinking red light resembling an unblinking eye watching her closely, along with the two team members following behind.

The initially trembling team member had calmed down a bit, still looking frightened but at least no longer shaking. As for the other team member, who wasn't human to begin with, Kaguya avoided paying attention to them. She had a vague feeling that focusing too much on that individual might lead to something unfortunate.

Surely, Maki must be in the command room right now.

The situation there was likely far more perilous, because the command room only had one player—Maki—and over ten others... none of whom were human.

No, she couldn't be certain. After all, every gaze in the command room was fixed on her at the moment. These entities seemed to embody the collective obsession of some group, endlessly replaying echoes of a moment from the past, much like the couple in the Shirakawa apartment complex. Thus, as long as her actions didn't stray too far out of line, she might be able to keep the eyes of those in the command room focused on her, maintaining the situation in a relatively stable state.

Still, this was just a hope.

As she pondered, Kaguya crossed the entrance and spotted a staircase leading downward. Beside it, red letters carved into the rocky wall formed a sign that read:

"Welcome to the Nutty Dutty Cave Scenic Area."

This was the entrance to the Nutty Dutty Cave.

It was the starting area of the dungeon their group was supposed to explore, according to the mission briefing.

However, based on the initial information, they were supposed to arrive at an actual tourist attraction, not a research facility like this one.

Kaguya understood that this discrepancy meant the dungeon was now fixed. The moment all three of them selected this dungeon and stepped inside, it had entered the fixed phase.

Unlike Maki, Kaguya had awakened in the medical examination room of the research facility.

Her assigned identity appeared to be that of a "voluntary" participant in some secret research project. According to the conversations around her, she was also playing the role of a death row inmate. If she successfully completed three exploration missions, her criminal record would be expunged, and she could return to society to live a normal life.

It was almost laughable. Kaguya didn't need much thought to conclude that none of the explorers in this program had ever survived. Even if someone had miraculously completed the three explorations successfully, their ultimate fate would still be death. Considering her current assigned identity, Kaguya had no doubt that if she obediently followed instructions, she was bound to meet the same end.

Therefore, she resolved that, no matter what, she must find a way to sabotage her headset later, cutting off communication. Only by doing so could she create a chance for her survival.

However, even that would only be enough to protect herself. As for Maki... how could she help her escape this dire situation? Maki's role seemed to be that of a researcher, a relatively safer position compared to Kaguya's. But escaping the current environment and completing this game would undoubtedly be much harder for her. Moreover, the research facility—one that wasn't mentioned in any of the mission briefings—was filled with bizarre humanoid entities. Did that mean something had happened here, leading to the death and transformation of everyone in the facility?

[C1, report your status.]

While deep in thought, Kaguya had descended a winding staircase into the cave. Just then, her headset buzzed with the cold voice of someone from the command room.

"I am about to pass the staircase at the entrance, officially entering the cave. My team currently... has a total of three members, no changes."

Kaguya recalled the standard responses she had heard during the personnel preparation briefing earlier and carefully replied to the command room's directive.

[Acknowledged, proceed.]

The next instruction from the command room quickly followed. Kaguya didn't sense anything unusual. For now, the situation didn't seem too bad.

Step—

The staircase under her feet came to an end.

A massive cave, clearly modified by human hands, unfolded before her eyes. The ground had been leveled, paths were constructed, lighting fixtures and benches were installed.

A chilling draft spread through the air.

She knew she had officially entered the Nutty Dutty Cave.

She took in the current scene of the cave.

"This is…"