Nigojū is a Japanese author best known as the creator of the light novel series The Detective Is Already Dead. Originally from Fukuoka Prefecture, he began writing light novels after becoming immersed in the medium during a year spent preparing for university entrance examinations. His early work included participating in dōjin circles and events such as Comiket, influenced by romantic comedy series like Oreimo, My Youth Romantic Comedy Is Wrong, As I Expected, and Saekano: How to Raise a Boring Girlfriend.

His professional debut came after winning the Grand Prize in the 15th MF Bunko J Light Novel Newcomer Award. The winning manuscript formed the basis for The Detective Is Already Dead, which was first published by Media Factory under their MF Bunko J imprint in November 2019. The title of the series originated from a single sentence the author thought of one day: Is there a detective on the plane? This line later became the opening of the story.

The series proved to be the foundation for a multimedia franchise. Nigojū is credited as the original creator across multiple adaptations. A manga adaptation illustrated by Mugiko was serialized in Monthly Comic Alive from May 2020 to October 2023, with six volumes published. A second manga adaptation, The Detective Is Already Dead: The Lost Memory, illustrated by Poni, ran from January 2021 to September 2022 and was collected in four volumes. An anime television series adaptation produced by ENGI aired from July to September 2021, with a second season announced for a future broadcast. The light novel series itself remains ongoing, with twelve volumes released as of late 2024. All primary works—the light novels, the main manga adaptation, and its spin-off—are credited to Nigojū as the original story author.

Regarding creative identity, Nigojū has noted that his influences are primarily romantic comedy light novels. In developing The Detective Is Already Dead, he has described how certain characters evolved during the writing process. The character Siesta was originally intended as a minor figure but became a central character following the manuscript's award success. Similarly, the character Yui Saikawa was initially planned to fill the role of the detective before the story took its final form. His pen name was inspired by the author Sanjugo Naoki, who derived his name from his age at the time. Nigojū, being twenty-five when he chose his name, originally considered Nijūgo but altered the kanji to its current form to avoid appearing presumptuous.

The thematic identity of his work often explores the tension between past adventures and a quieter present, with a structure that employs flashbacks and non-linear storytelling. The recurring motif of loss and memory is central to The Detective Is Already Dead, where the premise of a detective already deceased shapes the narrative.

In terms of industry significance, Nigojū represents a successful discovery through the MF Bunko J Light Novel Newcomer Award, transitioning from an unpublished writer to the creator of a franchise with light novels, multiple manga series, and an anime adaptation with a confirmed second season. His work has been published in English by Yen Press, extending its reach to an international audience.