The Fifth Horseman is the story of Keiji, a young Imperial Japanese Army (IJA) medic assigned to the infamous Unit 731's medical experimentation facility commanded by his father. Keiji has always believed Unit 731's work is wrong, but as a failed medical student he has become so consumed by his desire to earn his father's respect that nothing else matters. Everything changes with the arrival of a captured American pilot, whom Keiji soon befriends. Inspired by his new friend's courage, Keiji throws off the shackles of tradition to rise up against his father and bring Unit 731 to its knees.
