Shinobi: Heart Under Blade is a 2005 Japanese romantic drama film directed by Ten Shimoyama and written by Kenya Hirata.

Set immediately after the Japanese Sengoku period, Iga and Kouga, two mercenary clans have been waging a vendetta against each other over hundreds of years.

Attempting to consolidate his reign, he deliberately stirs up their feud by inviting the clans to choose their five best warriors to fight to the death.

Designated as the leaders of the two clans respectively, Kouga Gennosuke (Joe Odagiri) and Oboro (Yukie Nakama), who have secretly married, are unwillingly embroiled in the political plot.

Initially, being peaceful and knowing the preciousness of life, they try their utmost to prevent this meaningless and brutal fight by questioning the shogunate's motives.