The Esper Zodiark uses Darkja as its ultimate attack in the battle against it in Henne Mines. It deals intense Dark-elemental damage and may inflict Blind or Instant Death (the player can be hit with both, as the Blind status does not disappear when the victim is Knocked Out). The Quickening Concurrence Black Hole is visually similar to this spell.
The Ascian Nabriales uses Dark IV during the Chrysalis trial. He will use the Dark IV ability as his special attack during the battle twice. Dark IV deals strong field-wide unaspected damage to all party members, with its damage dependent on how many orbs he was able to absorb.
Darkja is the summon ability of the Hades (God) summon. The ability deals dark-elemental damage to all enemies.