There are several reasons you might want to remove the rear seat on your Mazda RX-8. You must remove it if you need to service the fuel pump, because there is an access hole located under the seat cushion. You may need to haul larger objects. Removing the seat back allows you to haul items in the trunk and rear cabin at the same time. No matter, what your reasoning is, you can remove the seat cushion and seat back without the use of tools.
Grab the left-upper corner of the seat back, and pull out on it. There is a press-in tab on the back of the seat that presses into the sheet metal of the trunk frame. As you pull on the seat back, the tab pulls free of the frame.
Grab the right-upper corner of the seat back, and pull out on it to release the second press-in tab.
Lift up on the seat back, and remove it from the RX-8.
Grab the left corner of the seat cushion, and pull up on it. This pulls the push-in tab out of the floor pan.
Slide your hand under the lifted portion of the seat, and slide it right until the tab gets tighter. Force the seat upward by pushing up on the bottom of it. This pops the second press-in tab out of the floor pan. Repeat this step until you remove the third and fourth press-in tabs.
Lift up on the seat cushion, and remove it from the RX-8.