Gintama

Twenty years before the story begins, in the late Edo period, mysterious aliens known as "Amanto" invaded Earth. A war between humans and the Amanto erupted immediately, with many samurai and Joi (reformation) patriots joining the fight. Witnessing the overwhelming power of the Amanto, the Shogunate ultimately surrendered to them, abandoned the samurai, and unilaterally signed unequal treaties allowing the aliens entry into the country. Subsequently, they issued the "Sword Ban Decree," stripping samurai of their swords and rendering them unable to resist. From then on, the Amanto ran rampant, and the Shogunate, influenced and even controlled by them, became a "puppet regime." In this era, one samurai lives happily with his companions in a whimsical, fantastical manner.