There are two hidden chests you need to find at Thresher Waterwheel.
Zack Palm -
Get to know your party members to unlock additional side story options.
Zack Palm -
In case you wanted an even bigger challenge.
I wouldn't say no to an Episode Vincent.
Grab every party member you can find and add them to your growing team.
Zack Palm -
Give yourself an advantage from the start.