Masamune Kuji is a Japanese novelist and screenwriter, primarily recognized as the author of the light novel series Hybrid x Heart Magias Academy Ataraxia, which was later adapted into a manga and an anime television series. He began his writing career in 2012, entering the 18th Sneaker Prize under the pen name Juzo with a manuscript titled Soul Synchronization Machine, which earned an award. Following this success, he adopted the pen name Masamune Kuji and reworked that manuscript into his debut work, Hybrid x Heart Magias Academy Ataraxia (titled in Japanese as Masou Gakuen HxH), which was first published in February 2014 under Kadokawa Shoten's Sneaker Bunko imprint. This series, illustrated by Hisasi, became his most notable creation, running for a total of fourteen volumes until its conclusion in September 2019.

The success of the light novel led to a multimedia expansion. A manga adaptation illustrated by Riku Ayakawa was serialized in Kadokawa's Comp Ace magazine from June 2015 to 2018, eventually compiled into four volumes. An anime television adaptation produced by Production IMS aired from July to September 2016, with additional original video animation (OVA) episodes released later that year. The English versions of the light novels and manga have been published by Yen Press.

Following the momentum of his debut series, Kuji launched another light novel series titled Ecstas Online in September 2016. His more recent work includes the Honey Trap Shared House series, with multiple volumes released in English by Yen Press throughout 2023 and 2024. Beyond his original light novel series, Kuji has also worked as a screenwriter for anime productions, contributing scripts for the series Hajimete no Gal. His creative work is consistently published under the Kadokawa Sneaker Bunko label, and his stories typically blend action, science fiction, and ecchi comedy elements, often focusing on protagonists with unique abilities that require intimate contact with female characters to unlock their full potential.