Based on a true story, "13 Assassins" revolves around the tale of a group of ronin (masterless samurai) who band together to take down a notorious lord, Kaito Shiota, known for his cruel and inhumane treatment of his subjects. Led by the fearless and skilled Shinji Higuma, the group of 13 assassins embark on a perilous mission to infiltrate Shiota's castle and put an end to his reign of terror.