Genuine Toyota OEM JZA80 / MK4 Supra & JZZ30 Soarer Rear Seat Cushion Lock.
These let the rear seats clip into the body of the car. Over time they can be worn and not clip the seat in tight or just break being plastic.
Note: This product does come in the OEM Toyota packaging, it was just removed for site image.
One is required for each side of the body of the car.