Takakage is a college student haunted by vivid, recurring dreams set in Japan's Sengoku era. In these dreams, he lives as Genshiro, a soldier deeply in love with a shrine priestess named Ayame. Their romance hurtles toward tragedy when Genshiro dies shielding Ayame from an enemy soldier, leaving her devastated. In her grief, Ayame attempts an immortality spell to save him but miscasts it upon herself, condemning her to immortality and centuries of solitude.

In the present, Takakage attends a festival with his stepsister Maiko and their friend Mayumi Hiragi, who practices fortune-telling. Mayumi predicts Takakage will soon fall in love with a beautiful woman. Later, Maiko reveals she experiences identical dreams about the Sengoku romance, blurring the boundary between shared subconscious and past-life memories. Takakage then encounters a woman named Chisato, bearing an uncanny resemblance to his dream Ayame, leading him to believe she is Mayumi's prophesied love.

Takakage's bond with Chisato deepens, but it is revealed that "Chisato" is actually Mayumi in disguise, attempting to confess her long-hidden feelings. Takakage rejects her romantic advances, unable to reciprocate. Concurrently, Ayame appears in the modern world, having endured over 400 years due to the failed spell. She recognizes Takakage as Genshiro's reincarnation and reignites their ancient love. Yearning for a normal life together, Ayame reverses the immortality spell but dies shortly after.

Following Ayame's death, Maiko confesses her own romantic feelings for Takakage and reveals a critical secret: they are not biologically related. This revelation resolves Maiko's earlier internal conflict over her taboo desires. The story concludes with Takakage and Maiko entering a romantic relationship.