stormblood DRK

-you should never drop Dark Side, unless there is an extremelly long boss phase you do nothing.
- dark arts can only be used under Dark Side, as some other skills.
- dark arts consume 25% of your MP.
- abyssal drain only heal you when powered by dark arts.

And all of that shows in the tooltips for the skills.

edit: drk heals tru DA-abyssal drain and grit soul eater.