Toaru Majutsu no Index: New Testament - Volume 18, Prologue: Connection Point - Destiny_Joint.

The outside world is filled with monstrous shadows. I’m so scared.I just want to stay in my safe house, forever…————————Unkillable phantoms and endless monsters abound. Yu Hong arrives here with a mysterious black mark. Using its power to strengthen everything, he gradually builds an absolutely secure zone of his own within his safe house.

Charlotte Meklen had crossed into the Fars Empire, seeking only to become a civil servant in a different continent. She wasn’t a combatant... But who would have thought that even clerical staff would end up on the battlefield!

A con-man and policewoman that are legends of their respective professions suddenly die, then are reincarnated and return to the Tang Dynasty of ancient China as little kids.

Accepting their second chance and forced restart, they choose to use the modern knowledge and specific talents that they have in their previous lives in order to live comfortably in this new life.

- Description from Novelupdates

It was a time where demons roamed the earth and chaos reigned. The story took place in Luoyang, the legendary capital of the times. During the night, one could find people holding on to their food with dear lives as they faced off against stray dogs, people with weapons in hand vowing to fight against Fate to their very last breath. There was bloodshed everywhere as some died meaningless deaths, while the strong tyrannized the weak and the truth was frequently hidden. Some of the citizens had completely lost their mind, while some died on their travels. Most importantly, the words of a certain youth caused much panic in the human world. It was a time of little warmth as nights in the capital were frequently accompanied by gusts of wind and rain, and it would be covered with snow during winter. Such were the days…

- Description from Novelupdates