i can explain the ranking system for you
at the end of a misson there are your 3 ranks
Clear Time
Stylish Points
Orbs Found
Time should be no problem the game gives you allot to get an S rank
Stylish Point is how well you do in fights
the 2 key factors in getting style points in fights is not getting hit and switching up your moves
if you spam the same move too much your style rank wont go up you need to switch up your moves in order for your rank to go up
if you get hit it will force your rank down and you wont get much style
the higher you rank is the more style you get from attacks
you also get more red orbs and proud souls
now to get a high rank for Orbs Found is a little annoying
basically all you have to do destroy objects
boxes, benches, chairs, the pods in the forest
brake everything you can
and find the hidden orb spots with nero's glowing arm there in the same spot every time so once you find them with nero you can get them with everyone
the last thing is your bonus or penalty
dying or useing items will give you a huge penalty to your end rank making it pretty much impossible to get a good rank
so if you die you might as well restart the mission
there are also 2 bonuses
no items and no damage
if you get no damage your pretty much guaranteed an S rank
to get an end rank of S you pretty much need an S for stylish points
and A's for the other 2
or an A for stylish
and S's for the other 2
if you do well your mission clear screen should look like this
i was lucky enough to not take damage when i got this
hope this helps you