Rui Tsukiyo is a Japanese novelist known for creating several light novel series that have been adapted into manga and anime. He is originally from Gunma Prefecture and began his writing career by releasing stories on the user-generated web fiction site Shōsetsuka ni Narō in 2014. His first series, Elf Tensei kara no Cheat Kenkokuki, won the Monster Bunko Awards Grand Award in 2015, leading to its print publication by Futabasha later that year.

Tsukiyo has created numerous works, many of which fall within the fantasy and isekai genres. Among his most notable original creations is The World's Finest Assassin Gets Reincarnated in Another World as an Aristocrat. This series began as a web novel in 2018 before being published in print by Kadokawa Shoten under their Kadokawa Sneaker Bunko imprint starting in 2019. The story follows a legendary assassin who is reincarnated by a goddess to prevent a hero from destroying a fantasy world. It was adapted into a manga in 2019 and an anime television series that aired from October to December 2021.

Another prominent work is Redo of Healer, which started as a web novel in 2016 and was officially published by Kadokawa Shoten in 2017. This dark fantasy revenge story received both a manga and an anime adaptation. Tsukiyo is also the original creator behind Dungeon Builder: The Demon King's Labyrinth is a Modern City!, a light novel series that began in 2016 and inspired a manga adaptation illustrated by Hideaki Yoshikawa, which concluded in 2025. His other works include Slime Tensei. Dai Kenja ga Yōjo Elf ni Dakishimeraretemasu, which was published as a light novel starting in 2017.

Tsukiyo's writing is recognized for its dark and violent content, frequently incorporating themes such as murder, revenge, and rape. He has stated that he prefers protagonists who do not hesitate and that his stories emphasize the protagonist's actions. Regarding Redo of Healer, he has explained that it was influenced by popular revenge stories on Shōsetsuka ni Narō and was a deliberate gamble, with the hope that its controversial nature would drive sales.

As an original creator, Rui Tsukiyo has achieved significant commercial success, with multiple of his light novel series being licensed for English publication and adapted into other media. His work has established him as a prolific and distinctive voice in the light novel industry, particularly within the isekai and dark fantasy subgenres.