As splinter and the turtles included usagi the samurai rabbit was teleport back in time. It was the past japan.

Michelangelo: dudes what happened

Usagi: I believe somehow we’ve been teleported back in time back to the past

Leo: before splinter was born?

Splinter nods: correct Leonardo this time where is my mother Nikki hamato is still a child and hasn’t married my father yet

Michelangelo smirks: cool we get to meet our gram gram in her childhood home

Rapheal : we’re not here to visit anyone Mikey we’re just need to figure out how to get back to our timeline

Donnie : I might suggest our only suggestion is going to splinter mother house and see if she knows anything

Usagi : I agree with donetello if we stay in the past we can caused more harm then good

Splinter: ok follow me I know the way as splinter leads his sons and usagi Nikki house