Shinji Ishii is a Japanese author known for writing the novel Toritsukare Otoko. The book, whose title translates to Obsessed Man, was originally published online in October 2001 through Biriken Shuppan. It was later released in print as a paperback by Shinchosha under their Shincho Bunko imprint in March 2006. Ishii was born in Osaka, Japan.

The author's body of work includes several other titles. Among his published books are Planetarium no Futago from 2003, Yuki-ya no Ross-san from 2006, and Mizuumi from 2007. He has also written Akazukin, Hitotsubu no Uchuu, and Shiirakansu. Additionally, Ishii contributed to the anthology Kimi ga Mitsukeru Monogatari Fushigi na Hanashi Hen.

Ishii is best known as the original creator of Toritsukare Otoko. The story follows a young man named Giuseppe, whom the townspeople call the Obsessed Man because he becomes completely absorbed in whatever catches his interest, to the exclusion of everything else. He falls in love at first sight with Pechka, a balloon seller who carries a quiet sadness. With the help of his mouse companion, Cielo, Giuseppe uses the skills he has obsessively learned over the years to try to solve the problems weighing on her heart. The novel has been adapted into a stage play four times.

The most significant adaptation of Ishii's work to date is a musical anime film produced by Shin-Ei Animation and distributed by Bandai Namco Filmworks. The film is directed by Wataru Takahashi, with a screenplay by Naoyuki Miura, character designs by Masatsugu Arakawa, and music composed by atagi from the band Awesome City Club. The film is scheduled to be released in Japan on November 7, 2025. Upon the film's announcement, Ishii commented on the process of seeing his words transformed into a visual medium, expressing deep appreciation for the staff's dedication to bringing the story to life.