First Stygian Diviner:Apocalypse - Chapter 293 Ciel, I Am Sorry -MR4

Kazuki’s life was painfully average—just another cog in the nine-to-five grind. His only escape? Binge-reading novels and no-lifing video games.Then he woke up inside one of those novels.Armed with unstable morals, unhinged humor, and a penchant for pettiness, Kazuki is determined to survive, thrive, and maybe cause a little chaos along the way.The world has no idea what’s coming.

Coming from the modern era, she was sent to a strange world. The body she possessed previously belonged to a young woman whose family was thrown away by their clan. However with the “Dan Fu Zong”, the inheritance from her old world, she steps on the path of cultivation, hoping to one day become an immortal.

- Description from Novelupdates

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.

Dynasties rise and dynasties fall, like the tide washing the sand.