Crescent Unit Plenum is an enemy from Crisis Core -Final Fantasy VII-.
As his name implies, he is part of Wutai's elite fighting force, the Crescent Unit. Its Shoot attack may inflict Stun on hit. The player should try and interrupt its attacks if Zack has low health. It's possible to steal Blizzard Blade from it.
Plenum is Latin and means a space completely filled with matter, or a state of fullness, a great quantity (of something).