The story is set in the mid-Edo period. Shogun Yoshimune Tokugawa often sneaks out of the castle with his retainer cat, Nyanmage, and walks around the town hiding his identity. His original purpose is to know the lives of the common people and help them with good government, but sometimes his sense of justice overrides him and he forgets his position and acts accordingly.

This time, they go undercover at a Kendo school rumored to be suspicious, posing as apprentices. The school was inherited by a samurai named Kotone Hori from a late father, but it has since been taken over by a corrupt official named Onigawara.

Nyanmage will not tolerate villains who prey on innocent people...
Together with the unconventional Shogun, he makes a big stand in Edo town!!