In the alternate Edo of Gintama, where alien invaders have forced samurai into a diminished role, the Shinsengumi serves as the special police force maintaining order. The peace is shattered when the demonic vice-commander, Toushirou Hijikata, acquires a cursed sword from a blacksmith. Rather than enhancing his legendary combat skills, the blade rewrites his entire personality, transforming the hard-boiled, mayonnaise-obsessed officer into a useless and pathetic otaku with no redeeming qualities.

As Hijikata struggles to break the curse, an ambitious new member of the Shinsengumi named Itou Kamotarou returns to Edo after completing a long mission. Itou brings advanced weapons and prized swords as gifts, earning a warm welcome from Commander Isao Kondo and quickly rising in prominence within the organization. However, Itou seizes the opportunity presented by Hijikata's weakened state to launch a devious scheme for power. His plan to depose Hijikata and take control of the Shinsengumi proves more treacherous than anyone anticipated, throwing the entire organization into a crisis that threatens not just the police force but the stability of Edo itself.

The conflict forces Hijikata to confront the curse while battling Itou's faction from within. Gintoki Sakata and the odd-jobs Yorozuya team become entangled in the affair, leading to an alliance between the laid-back former samurai and the beleaguered vice-commander against a common enemy. The story explores themes of loyalty and betrayal as the Shinsengumi's bonds are tested to their breaking point, with Commander Kondo serving as the stabilizing force holding the group together. The arc concludes with a resolution that reaffirms the Shinsengumi's unity while leaving lasting consequences for the characters involved. This theatrical compilation brings together episodes 101-105 of the original television anime series.