Just finished Uncharted and thought I'd have a crack at this. Given it's a Japanese RPG type thing any advice for getting the most out of it from a single play through without delving too much into gamefaqs.
I did glean that the goal is to finish missions as quickly as possible, and noticed a very large boost from swapping from a careful balanced multi character advance to a suicidal close range headshotting rampage with Welkin.
Since it appears you can't redo missions it looks like you should repeat missions via load/save to get the highest scores you can.

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