Satomi Tsubaki, a high school student and covert operative of the Koga ninja clan, masquerades as a classmate infatuated with the protagonist, orchestrating a seemingly innocent date to her residence. Beneath this facade lies a calculated assassination plot targeting the heir of the rival Iga clan. During the rendezvous, Koga agents ambush the protagonist, but their scheme collapses when his allies intervene.

Captured and imprisoned after the mission’s failure, Satomi chooses suicide over divulging clan secrets, silencing herself permanently. Her mission forms a critical thread in the Koga’s larger conspiracy: framing the Iga for their own leader’s murder to legitimize all-out war between the ancient rival factions.