Darkside is an action unlocked by questing at level 30. It's available for Dark Knight.“
Increases damage dealt by 20%. MP regeneration stops during battle and Refresh statuses granted by others have no effect.
Effect ends upon reuse.
— In-game description
Similar to a paladin's Sword Oath, this stance is more of an attack-based stance. You take on an aura-like effect known as Darkside, which halts your ability to recover MP through any way other than your own abilities. While in this stance, you will not be able to receive MP healing support from party members. There are weapon skills which restores MP so it’ll be very important to make good use of those skills to manage MP. Darkside can be activated while in Grit stance.