Ghost of Yōtei tells the story of Atsu, a young woman whose family is massacred by outlaws known as the Yōtei Six, led by Lord Saito, in a brutal event called the Night of the Burning Tree in 1587. Left for dead, Atsu survives, becomes a hardened mercenary for 16 years, and returns to Ezo (Hokkaido) in 1603 seeking vengeance, hunting down each member of the Yōtei Six. Her journey transforms from pure revenge into a quest to protect the living, culminating in her finding peace and a new purpose as a guardian, breaking the cycle of violence.