Dxd: A demon Among Devils - Chapter 29: []:

Dong Xi transmigrated, but she was neither the female lead nor the villainess, but a tragic side character in a book. Even though she was a proper rich daughter, her mother used her as a substitute for her youngest sister, and sent her to train as a cultivator at the top cultivator sect in the world. Though she was initiated at eight years old and trained for eight years, she was talentless and didn’t have much experience. Eventually, her younger sister was recruited because of her outstanding talent, while Dong Xi was banished after it was revealed that she was just a substitute.

After that, someone caught her, imprisoned her, and tormented her for two years just because she was attractive. Though she was rescued by a senior disciple from the cultivator sect, it turned out that he did it to avenge her younger sister, and tortured her to death. When Dong Xi transmigrated, it was just after she was initiated and began life as a cultivator. She decided that she would do her best, improve her cultivation, and survive! Eating? Sleeping? All that was a waste of time! If there was a cultivator who practiced sword cultivation a thousand times per day, she would do two thousand!

Eight years later, when her younger sister was recruited for her talent, Dong Xi promptly packed her bags and left, leaving the cultivator sect panicking and wondering who had taken her away! Su Cheng, the most powerful demon lord: Who dares harm my beloved wife?! This means war! Dong Xi, still running away: What? Who are you? Su Cheng: Don’t you remember the snake you counted stars with years ago, beloved?

A teenager who unexpectedly gets transported to the modern world from ‘the world of the immortals’ . He finds himself in the body of an ordinary guy. He wants to go back to his world and for that, he will have to practice to get stronger and investigate the reason why and how he crossed through to this world.

- Description from Novelupdates

The world is terrorized by the powerful Black Witch who has been sealed in the moon. Every ten years, the night of Hexennacht arrives and a chosen witch must battle the Black Witch in hopes of finally defeating her.

As the current decade’s Hexennacht approaches, a mysterious girl named Kagami Kagami arrives and meets Horinouchi Mitsuru, the daughter of the previous Hexennacht representative.

It takes place between Kyoukai Senjou no Horizon and the City Series, two other series by the author.

Two heroes of the game Legend of Heroes 2 who were rotten waters*.