Takumi Yanai is a Japanese novelist best known as the creator of the GATE fantasy series. His professional name in Japanese is written as 柳内たくみ. Prior to his writing career, Yanai served as a Self-Defense Force officer until his retirement in April 2006. Following his military service, he began writing fiction, initially using the pen name とどく＝たくさん to publish a series titled Fantasy Self-Defense Force on the Arcadia website, which he completed in June 2009.

Yanai’s professional debut came in April 2010 when the online series was published in print by AlphaPolis as a single-volume novel retitled GATE: Jieitai Kanochi nite, Kaku Tatakaeri, commonly known as GATE. This work became his representative creation and laid the foundation for his career. He continued to expand this universe with a sequel series, GATE Season 2: Jieitai Kano Umi nite, Kaku Tatakaeri, which began publication in 2017. The franchise’s popularity is reflected in its circulation, which has surpassed 7.5 million copies for the novels and manga combined.

Beyond the GATE series, Yanai has authored several other works that often blend historical settings with modern elements. He wrote the five-volume series Sengoku Sniper, published by Kodansha between 2012 and 2015, which follows a modern sniper navigating Japan’s Warring States period. His other standalone novels include IOTA: Tactical Mechanical Infantry, a single-volume work released in 2016, and Walhalla: e-Senjo no Senso Geijutsu, published in 2018. He also wrote The Sniper Ice Wind: Snow Fairy and the White Death, a novel released in two editions by AlphaPolis in 2012 and 2013.

Yanai’s most significant contribution to anime is the television adaptation of his flagship work. The first season of GATE aired from July to September 2015, followed by a second season from January to March 2016. The continued relevance of his original story is demonstrated by the announcement of a new anime adaptation, GATE 2: Tides of Conflict, which is based on his GATE Season 2 novels. This project was announced in 2025 to commemorate the franchise’s 10th anniversary. While Yanai is the credited original creator of the source material, his direct involvement in the production of the anime adaptations is as the author of the underlying novels rather than in a direct production role such as direction or screenwriting.

As a creator, Yanai’s work is distinguished by its fusion of modern military elements with fantasy and historical fiction, a perspective likely informed by his own background as a Self-Defense Force veteran. His narratives frequently explore the intersection of contemporary military forces with other worlds or different time periods, establishing a recognizable thematic identity within the light novel and anime industries.