The story focuses on an eccentric samurai, Gintoki Sakata, his (partial) apprentice Shinpachi Shimura, and a teenage alien girl who's from one of the strongest races in existence: yato. All three are "freelancers" known as the Yorozuya. They search for work in order to pay the monthly rent. The story takes place in the Edo Period, but instead of the Europeans invading in the late 1860s they are invaded by aliens, which they call Amanto.
Gintama arc are either parody or serious battles, but there aren't super powers or special techniques, the fights are quite magnificent.
About this week chapter: could that guy that we saw on the flashback be Gintoki's father? And damn, this arc is really good.