Kōki Fuyutsuki is a Japanese author best known as the creator of the light novel and manga series The Too-Perfect Saint: Tossed Aside by My Fiancé and Sold To Another Kingdom. Fuyutsuki is the original writer behind the franchise, which began as a web novel serialized on the user-generated publishing platform Shōsetsuka ni Narō, running from July 18, 2020 to January 19, 2022. Following its online success, the series was acquired by the publisher Overlap, who began releasing it as a physical light novel under their Overlap Novels f imprint on April 25, 2021, with illustrations provided by the artist Masami. As of March 2025, eight volumes of the light novel have been released.

The story of The Too-Perfect Saint centers on Philia, a highly capable saint whose engagement to a prince is broken off, leading to her being sold to a neighboring kingdom. There, she discovers a more appreciative environment while her original homeland begins to crumble without her support. A manga adaptation of the series, illustrated by Mago Ayakita, began serialization on Overlap's Comic Gardo service on November 5, 2021. Both the light novel and manga have been licensed for English release in North America by Seven Seas Entertainment. The growing popularity of the franchise culminated in the announcement of an anime television adaptation produced by the studio Troyca, which premiered in Japan in April 2025. In addition to this main series, Fuyutsuki is also credited as the author of another light novel and manga series titled I Abandoned My Engagement Because My Sister is a Tragic Heroine, but Somehow I Became Entangled with a Righteous Prince.

The creator's works often center on heroines who are exceptionally competent yet undervalued by those close to them, exploring themes of rejection, self-worth, and finding a new place to belong. The narrative of The Too-Perfect Saint in particular focuses on the consequences of taking a capable individual for granted, as the protagonist's former home rapidly declines without her diligent efforts. This premise has resonated with a wide audience, and the light novel series has achieved significant commercial success, with cumulative print copies reaching 1.5 million as of its anime announcement in late 2024. With a complete multimedia franchise encompassing the original web novel, a published light novel series, a manga adaptation, and an anime, Kōki Fuyutsuki stands as a notable example of a creator who successfully transitioned from an online writing platform to a major publishing and animation production.