In Kyoto, Japan, near the end of the Edo period, a young boy is being chased through the streets at night by a pair of revolutionaries loyal to the Emperor. Hiding in an alley, the boy is horrified to witness his pursuers' brutal murder at the hands of demonic looking men with glowing red eyes, who laugh maniacally as they hack their victims to pieces. When the fiends turn their attention to the boy, his life is only spared by the timely appearance of two samurai belonging to a group of powerful warriors loyal to the Shogun, known as the Shinsengumi. Unsure just where the boy's loyalties lie, the Shinsengumi take him into custody and return him to their headquarters.