Kyoukai Senjou no Horizon - Volume 7C, Chapter 68: Good Listener Below the Roof

Kaidan (Kaidan refers to eerie tales of strange, mysterious, rare, or bewitching ghosts and monsters from Japanese folklore.) feed on cognition, wield information as weapons, and use information as currency, existing between the peculiarities of neither life nor death.They exist in human rumors and dwell in the shadows of the world.“Does this mean I will become a Kaidan?”In ancient times, they were worshipped as deities, empowered by faith.“Then I am a deity!”In more recent ancient times, they were regarded as demons and fed on fear.“I will become the master of Kaidan!”However, as the tides of time washed over, they gradually vanished, leaving behind only texts considered to be delusions.“To restore the glory of Kaidan is an undeniable duty of ours.”But you are not yet a Kaidan, hmm, nor a person.“Well, becoming a Kaidan counts as success.”

It begins on the mountain.

With the glint of a knife, a flash of steel in the hands of a sworn brother. A betrayal.

Stabbed and pushed down the mountain, Zi Chen lied within the red-stained snow, left to die.

This is where it begins; he is given life by lightning,
baptized by thunder.

Those who had once betrayed him should all suffer in his cruel revenge.

- Description from Novelupdates

Cho Ryu Hyang was good at math from a young age. When he enrolled into the The Theoretical Maths and Martial Arts School, the teacher, Jo Gi Chun, recognized Cho Ryu Hyang’s talent immediately and took him in.

An unexpected journey took a group of university students into a secret room from which, upon returning, they began to disappear one by one. In order to unravel the mystery, they joined forces, traversing heaven and earth, diving deep into seas, crossing the farthest corners of the world, and even daring to time travel, only to find that behind each puzzle lay yet another.