The Speedrun Manual of Miss Witch - Chapter 27 - Standard Procedure at Charlie Bank (Part 1)

The unparalleled Demon King Ye Xuan, who was able to heal the death or the living alike and holder of the medicine Holy Scripture, was betrayed and killed by his fellow Demon Kings. But he reincarnated into the body of Ye Xuan, the prodigal son of the Ye family and vowed to himself that he would return to his peak and take back everything that belonged to him!

- Description from Novelupdates

[WARNING: MATURE CONTENT 18+. Contains Netori, No rape. No Yuri]

A seemingly ordinary training exercise led Chen Jian and his squad into a completely different time and space.In the post-apocalyptic world, monsters run rampant, and the surviving humans struggle to live under their terrifying claws.To fight the monsters, the living have abandoned everything.Human nature no longer exists; beastliness is the mainstream.To defeat them, one must first become them.-----------------Chen Jian was supposed to be like the others here, pursuing the maddening evolution.But, when the tungsten-core armor-piercing round first penetrated the Kui Niu's keratin armor, he suddenly discovered...Perhaps there is another way to stay alive?

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.