Sora Nakamura, a post-graduate in medicine from Ireland, is hurled into the complicated world of feudal Japan after her co-worker and best friend Sasuke drags her into his research. When Sora saves the life of Shingen Takeda, a great and previously presumed dead daimyo of the Sengoku era, she is recruited into his forces and trained in the techniques of the ninja. As she navigates the kill-or-be-killed, wealthy-on-top world, making friends, rivals, and enemies along the way, she falls into a dangerous and near-inescapable trap. All that she knows and loves is put at risk as past mistakes resurface, and Sora has to make life-changing and ending decisions if she wants to accomplish her aim-survive.