I couldn't miss the chance to practice my drawing!
Onyx Wave (漆黒, Shikkoku?, lit. Pitch Black), also known as Darker Side or Black Bane, is a recurring ability in the Final Fantasy series. It is an attack usable by Dark Knights and is a powered up form of their signature Souleater.
In the games where it appears, Souleater strikes one enemy while Onyx Wave hits all enemies, but Onyx Wave consumes much more HP to use.
Darker Side is an ability usable by the Dark Fencer. It consumes some HP to allow the user to attack all enemies.
The Dark Knight learns Onyx Wave at job level 5. It consumes a third of the user's max HP to attack all enemies.
Non-Final Fantasy guest appearances
In Bravely Default and Bravely Second, Black Bane is the job level ability for the Dark Knight asterisk. Both games involve the player character sacrificing 30% of the user's maximum HP to unleash a dark physical attack on all enemies.