Shinrei Tantei Yakumo - Volume 2 Chapter 1

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates

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.

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

Kaius just wanted to unlock his class - instead, he restarted the apocalypse. After years of training, Kaius has barely acquired the first two of his family’s legacy skills. Powerful and vanishingly rare, the method of creating them is a secret people would kill for. Now they might be the only thing that keeps him alive. Narrowly surviving a bandit ambush, he gets trapped in the Great Depths- a world spanning dungeon. To escape, he will have to slay one of the Guardians that defend the exits; a feat no one without a class has survived. Ever. If that wasn’t bad enough, if he succeeds he will reignite a forgotten trial that nearly ended civilization. -Runic-Tattoo Wizard/Spellblade in a world of sorcerers -Exceptional MC, with some initial Slow Burn elements -Large scope, inspired by epics such as Azarinth Healer, BTDEM, PH, and more. -Third Person POV, with a 99% MC focus -Numbers go brrrr -Attack Badger (Friendly?) -Battle maniac MC who is not a murderhobo -No harem, romance, or VR