Kouji Seo is a Japanese manga creator born on July 26, 1974, in Shobara, Hiroshima Prefecture. He began his career in 1996 when his one-shot manga Half & Half received a notable rookie award from Weekly Shōnen Magazine, leading to his debut in Magazine Fresh. Early in his career, he worked as an assistant to Tsukasa Oshima, the creator of the sports manga Shoot!

Seo’s first serialized work was W's, a tennis-focused manga published in Magazine Special from 2000 to 2001. He subsequently launched Cross Over in Weekly Shōnen Magazine in 2002, a series that combined basketball with high school romance. His first major critical and popular success came with Suzuka, which ran from 2004 to 2007. This series centered on a high school track and field team and was adapted into an anime television series in 2005, marking his first work to be animated.

Following Suzuka, Seo created A Town Where You Live, serialized from 2008 to 2014. This long-running romantic drama was set partly in his own hometown and received a television anime adaptation in 2013. He followed this with Fuuka, serialized from 2014 to 2018, which served as a narrative sequel within the universe of Suzuka and was adapted into an anime in 2017. In 2021, he concluded Hitman, a series set in the world of manga publishing, and simultaneously began his next work, The Café Terrace and Its Goddesses, which has also been adapted into an anime. In 2026, Seo began serializing his newest work, Ano Shima no Uminesō, in Weekly Shōnen Magazine.

Across his career, Seo has demonstrated a consistent artistic identity centered on romantic dramas. Many of his major works, particularly Suzuka and Cross Over, blend themes of high school romance with sports such as track and field or basketball. He has noted in interviews that his own experience on his high school track and field team and his interest in baseball influenced his storytelling. His narratives frequently involve complex romantic developments and love triangles, often featuring heroines with distinct short- and long-haired designs. He has cited Fujiko F. Fujio, creator of Doraemon, as a primary inspiration for becoming a manga artist

A notable characteristic of Seo’s bibliography is the shared universe present across several of his works. Characters from Suzuka, A Town Where You Live, Fuuka, and Hitman appear in each other’s stories, with settings and locations recurring across these titles. He has stated that incorporating characters from previous works helps him acclimate to new series. Beyond manga, his creative contributions extend to character design for other media, including a 2009 package illustration for High School Girl Kimchi and artwork for the Fire Emblem Heroes video game. For the Fuuka anime adaptation, he also wrote the lyrics for the series’ opening and ending theme songs. In 2021, a retrospective exhibition was held in Tokyo to celebrate the 25th anniversary of his professional career.