It's been 10 years since the Amanto war took place, with the 4 Legendary joui members losing the war, Japan declared an alliance with the Amanto. Legends says the 4 joui members are still around to this day

You wake up like usual, In the heart of japan Edo town more specifically the Kabuki district. You see the usual trio the red haired girl "kagura", glasses boy "Shinpachi", and silver haired man "gintoki" with their huge dog being a ruckus as usual, while the shinsengumi patrolling town