The Gate Traveler - Chapter 22B5 - : The Full Set

After picking up a phone on the streets, Feng Yuchen was sent to the world of High School of the Dead. He, along with 100 people, have to travel through various worlds, fight and solve quests in order to survive.

Whoever dies in that world, would be teleported back to the real world without memories of what happened before and die in an accident one year later.

- Description from Novelupdates

There’s an ancient saying in Great Ruins, ‘Don’t go outside when it’s dark.’

After 20 years of dedicating his life to opera ever since he had quit the performing arts high school, he had failed at an interview. Losing his motivations, Jo Yunjae depended on alcohol to live out his days until one day, he had been sent back 20 years in time, to the day before his high school admission.

Liola—the best assassin in his world—has vowed to kill no more. He was being chased by an assassination organization when he accidentally dropped into a parallel universe: through a dimensional gate and into poor teenager Kaiser’s apartment. Instead of going to the government shelter for lost dimensional travelers, Liola and Kaiser wind up going to school together.

Liola has been trying his best to live the life of an ordinary person, but after certain things happen one after the other, he begins to realize that being an ordinary person could be harder than being an assassin.