Matabar - Chapter 20 - Water and fire

Various monsters came out from mysterious gates that appeared all over the world. Along with this incident, humans also gained power and were called hunters.

Radmilo Laiv is a hunter with the power to control time. He spent his life serving the world government and becoming a hero. However, he was killed because his power was considered a threat to the government.

It was a stroke of luck that Radmilo could return to the past because of his powers. In this life, he doesn’t want to be a hero anymore. Should he play the evil role and become a villain?

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

After dying in an oddly anticlimactic vending machine accident, Kazuki Ren is reincarnated in the demon realm—not as a hero, not as a villain, but as the only human male student enrolled at the mysterious Academy of Ruin, a school where all the professors are demon lords and all the students are powerful, beautiful she-demons.Ren is told he has one task: survive.But there’s a catch. The Academy’s darkest secret is about to awaken, and Ren holds a hidden power that could either destroy the demon world... or rule it.Now surrounded by seductive demons with hidden motives, eldritch tomes, forbidden dungeons, and twisted exams, Ren must master his ability—or be consumed.Magic, mystery, danger, and temptation await in this dark academia harem fantasy.

After transcending to a new world, Ye Xuan miraculously obtained the Swallowing System.