Shinobi: Heart Under Blade is a 2005 Japanese romantic drama film directed by Ten Shimoyama and written by Kenya Hirata. It is an adaptation of Futaro Yamada's novel The Kouga Ninja Scrolls, although the characters are highly altered. It depicts the clash between two ninja clans, Iga and Kouga, and the fated love between Gennosuke (Kouga) and Oboro (Iga). The film's theme song was "Heaven" by Ayumi Hamasaki.

The film was released by Shochiku on September 15, 2005. On February 6, 2007, Funimation released the film on home video in the North America. The contents of the DVD is a 2-Disc Set with the main movie available in Japanese and an English dub. The 2nd Disc contains Special Features and making-ofs. All of the films are subtitled in English.