PityOnU - I was a seat design engineer for Toyota. The Rear Seat Cushion (the part that is sat on), that I designed (and this is fairly common), had some rods that form a sort of hook shape the stuck out the rear up under the Rear Seat Back (could not be seen in normal install position. And then there were 2 wire shapes that stuck downward into some clips in the floor.
Pop those 2 from hooked wires out vertically, and the seat slid forward and removed. Probably the same in the Mirage. It does look spacious with the Rear Seat Backs folded horizontally. I'll remember this if I'm ever needing those seat to fold flatter down.
Edit - I missed this page of replies. Seems the above was already answered.
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View my fuel log 2020 Mirage ES 1.2 manual: 42.4 mpg (US) ... 18.0 km/L ... 5.5 L/100 km ... 51.0 mpg (Imp)