I couldn't sleep because of the friggin backseat stuff and decided to google the damn car.
There are different versions of it, with and without backseat.
it's this version, only that shuu's is dark blue:
[link]So it's solved, it does have a backseat, but they're really really small and recommended for... Well yes. xD
And they can only be reached through climbing behind the front seats. =3
I'm sure of it, because Shuu's car had such a second, smaller window. xD
Now I can rest in peace, good night. xD