Gintama: Nanigoto mo Saisho ga Kanjin nanode Tashou Senobisuru Kurai ga Choudoyoi

Synopsis

The arrival of alien invaders known as Amanto has led to the downfall of Japan's samurai, stripping them of their swords and dignity. As the nation suffers under Amanto oppression, a faction leader named Kotarou Katsura seeks to restore the samurai's honor through forceful means, planning an assault on the peace-keeping Shinsengumi with a powerful mecha. Unbeknownst to them, Gintoki Sakata and his companions, enjoying a peaceful cherry blossom viewing, find their tranquility shattered when the Shinsengumi confront them over the prime spot. What begins as a dispute over flower-viewing quickly escalates into a chaotic confrontation, resolved through a surprisingly violent game of rock-paper-scissors.