君がため、恋し乱れし月の華

This is the Aoba province, located a short distance away from Edo. The edges of its north borders are mountainous, and to its south is a vast ocean. The citizens of Aoba live peaceful lives in its naturally abundant land.

Keika is a ninja working for Katsuragi Masakage, who is the chief retainer of Aoba province's feudal lord Aoba Yasutsugu. Tasked with guarding the feudal lord, Keika and her partner, Shinya start their mission.
Calm times.
Days filled with laughter.
Living without the faintest shadow of unease, their lives suddenly change for the worse.

One rainy day...
Keika visits a room and witnesses the dead and cold body of the feudal lord.
"The death of the feudal lord."
That very event turned the tides of not just Keika's fate, but the fates of everyone around her.

Working alongside her partners, Keika begins to investigate... but what truths await her in the end?

Otome Jikan