Gintama is an anime adaptation of a comedy manga written by Hideaki Sorachi. In the middle of the nineteenth century, first contact with aliens takes place - alien ships land in Japan. They arrive on Earth in order to capture it. Swords and guns are powerless against the technology of the future, and the shogunate submit to the superior power of the invaders.
Even more absurdity can be found at the Gintama channel.