Time setting is the Age of Warring States. The samurai were not the only ones whose lives were constantly in danger. The ninja also existed in the harshest environments, as they accomplished their missions from the shadows through acts of information gathering within enemy territory and influencing others to their side. Since their duty was to return home alive from their missions, ninja lived a long live. The ninja overcame the turmoil of their time period through high physical abilities and an unyielding spirit. Teruhisa Komori, a psychiatrist, is unraveling the secrets of the ninja’s spirit, techniques, and physique, as this could be the hint for the modern people living in a stressful society to learn how to live.