Okayama to Takamatsu

We plan to go to Takamatsu from Okayama by JR Pass, foa day trip to see Ritsukien Garden.
Wikipaedia shows JR Marine Liner train sets as having reserved seating, and bi-level cars.
Is it possible to reserve seating in the upper deck of the bi-level car, or is that the Green car?
Many thanks

Most cars are 1-storied and non-reserved. Just one car is 2-storied and reserved. The upper floor is Green Car and the lower floor is ordinary class.

... which does not mean you can't take it, it just costs a paltry 980 yen.

The view from single level cars is fine. The garden is wonderful but a distance from the station. There is a tourist information at Takamatsu station and it's worth checking which bus stop you need. I messed up once & ended up at the Aeon Mall. Did some good shopping though :)

Thanks everyone!! Sounds excellent Stan Norrell. We shall ask at Okayama the day before we go.
Thanks again