I couldn't finish 'em. Looks like this's gonna get complicated.
Two appear as bosses in Mission 3-2-5. They can use Gravity and Whirlwind (which is like Gravity, except it comes with an animation and is unavoidable). The player should hit them with Gravity or Graviga once or twice, then finish them off with sword attacks.
G Deleter appears in Final Fantasy Trading Card Game.