Kubonouchi made his professional career debut in 1986 with the short story Okappiki Eiji published in the manga magazine Shōnen Sunday.
From 1988 to 1991, he worked on his first series, Tsurumoku Dokushin Ryō, which was in 1991 made into a movie with Kōyō Maeda (ja) in the leading role.
His second manga series, Watanabe, was made into a television series in 1993, directed by Kiyoshi Kurosawa.
After a 7-year hiatus, Kubonouchi began Chocolat, a story about a former mob boss, just having been released from the prison, who befriends a 16-year-old girl. Chocolat was published from October 1999 to September 2003 in Big Comic Spirits. In 2003, the manga was made into a successful 45-episode television drama.