In an era where aliens have invaded and taken over feudal Tokyo, an unemployed samurai finds work however he can.

Okita’s older sister, Mitsuba, visits the quarters of the Shinsengumi to announce her marriage to the trader Kuraba Toma. The two siblings spend time together. Mitsuba worries that her brother has no friends and in order to assure her, he introduces Sakata Gintoki, who happened to pass by, as his best friend. Meanwhile, there are reports of strange boats going in and out of Edo. Hijikata Toshiro investigates this and it turns out that the incident has an unexpected link to Mitsuba.