A female assassin, Masami, nicknamed Yasha, receives a job. The murder appears to have been carried out brilliantly with Yasha's brilliant techniques. However, Amimoto, the murdered man's younger brother, relentlessly pursues Masami.

Having lost consciousness and collapsed, Masami is nursed back to life by Kenji, a doctor. When she regains consciousness, she has no memory of the past. As she stays at Kenji's house, the two gradually become attracted to each other. Just as Masami is beginning to feel satisfied with her current life, someone breaks into Kenji's house. However, Masami easily defeats the two men. A dark shadow haunts Masami. Nightmares every night. Who and what is she? Masami tries to find the answer somehow, but one day, a woman tells her the truth...