80 Years Of Signing-In At The Cold Palace, I Am Unrivalled - Chapter 16: This World Is Going to Become Chaotic

After traveling for three years, Lin Yu was drawn into a horror game unexpectedly.

However, he discovered one thing.

The dungeon boss feared by countless players turned out to be the little loli who called her big brother next door.

then.

In the horror hospital, the director of the hospital turned out to be the uncle downstairs who made him and his granddaughter fall in love.

In the bloody slaughterhouse, the existence known as the bloody butcher turned out to be the uncle upstairs who wanted him to be his brother-in-law.

In Changteng Ghost School, the woman who frightens countless students is actually the long-legged sister Yu who invites her to her house for dinner whenever she has nothing to do.

…

Traveling through three years, you told me that this place is actually a horror game world?

(Introduction is weak, please read the text)

- Description from novelbuddy

This is a prequel to the anime movie To Aru Majutsu no Kinsho Mokuroku – Endymion no Kiseki.

Just before the completion of the Academy City space elevator “Endymion”, the main characters Kamijou Touma and Index encounter a level 0 girl named Arisa. The Magicians are after Arisa, and they attack Academy City. A female leader named Shattoaura leads a unit from Academy City against the attack. Kamijou and Index learn from Stiyl that Arisa is key to a brewing war between the sides of Magic and Science. When science and magic cross paths, the story begins with Endymion as its stage!

As a boss with space plant abilities in the apocalypse, Lu Yao once traveled to the future, became the director of a nursery school that was about to close down, and became a rare animal human on the verge of extinction.
The food she made at random can cure the genetic disease of the cubs in the welfare home. She punched the cubs’ scum fathers and scum mothers, and kicked the remarried families who abandoned the cubs.
It is such a good kindergarten successor dean, who is attracted by that single cool imperial marshal!
Since then, the barrage in the live broadcast room has become:
Imperial Citizen A: Dean A, I really want to marry.
A certain big black dragon: Shut up! This is your marshal’s wife!
CP: Dean Lu Yao, who is extremely protective of short-sightedness and loves cubs, X the imperial marshal Helanjia who loves Shang Yunxi more than cubs
Brief: There are no bad cubs, only bad big ones.

- Description from novelbuddy

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.