Lucavi

The Lucavi (ルカヴィ, Rukavi) are a group of demons from Final Fantasy Tactics, who are working in secret under the cover of the Church of Glabados to revive their dead leader, Ultima the High Seraph. There are at least seven Lucavi, though one of them, Elidibus, is not necessarily connected to the other six. Each Lucavi is connected to a shard of Auracite, called a Zodiac Stone, which serves as a conduit for that Lucavi to exist in Ivalice. Each Lucavi also has a human host, allowing them to interact with others in Ivalice without drawing attention. The Lucavi are capable of switching between human and demon form via their Zodiac Stone.

All Lucavi return as Espers in other Ivalice games, notably Final Fantasy XII and Final Fantasy Tactics A2: Grimoire of the Rift; though Elidibus is known as his summon Zodiark.

The Identities of the Lucavi
The symbol of the Zodiac Braves contained these names written in ancient Ivalice script, and there are other names as well, though they will never make an appearance; most probably they were retconned in accordance to the beings that became associated with the six remaining signs. While unofficial, the retcon of Tactics would most likely identify the other six Lucavi as the remaining six Espers from Final Fantasy XII. This might not be a retcon, however, as the symbol of the Zodiac Braves was only ever seen as a sculpture in Final Fantasy Tactics and may well be an artistic creation within the context of the game (indeed, humans from Ramza's era had no idea who were the actual Zodiac Braves, and could have invented names similar to how demons from real world legends always have multiple names and varying status in the demon hierarchy).

Underlings
The Lucavi employ many underlings, the most notable of which are the Archaeodaemons and Ultima Demons. Both are of considerable power, and the Ultima Demons can even cast the spell Ultima. During the battles against Ramza, Belias summons Archaeodaemons to help him, while Ultima summons Ultima Demons to help her. In addition, Celia and Lettie, who serve Marquis Elmdore, are really Ultima Demons, and if defeated in human form during the battle with Elmdore, will transform in their demon form, and continue fighting. It is likely that Loffrey is also an Ultima Demon since Ramza felt the same feeling in Loffrey's presence as with Celia and Lettie. Both Archaeodaemons and Ultima Demons were summoned by Folmarv to help the Undead Zalbaag.

Cúchulainn the Impure (Queklain, the Tainted King) is associated with the Scorpio Auracite, and has possessed Cardinal Delacroix.

Belias The Gigas (Velius, The Warlock) is associated with the Aries Auracite, and has possessed Wiegraf Folles.

Zalera the Death Seraph (Zalera, the Angel of Death) is associated with the Gemini Auracite, and has possessed Marquis Elmdore.

Adrammelech the Wroth (Adremelk, the Ghost of Fury) is associated with the Capricorn Auracite, and possesses Dycedarg Beoulve.

Hashmal Bringer of Order (Hashmalum, the Regulator) is associated with the Leo Auracite, and has possessed Folmarv Tengille.

Ultima the High Seraph (Altima, the Bloody Angel) is associated with the Virgo Auracite. She originally possessed Saint Ajora, but upon his death was stuck within him, and as such the other Lucavi tried to revive her original host and transfer her to a new one, Alma Beoulve.

Elidibus the Legendary Wizard also takes the form of a Lucavi, but retains his own name. He does, however, summon Zodiark, the Esper who represents the sign Elidibs wields, Serpentarius.

The Attempt to Revive Ultima
Ultima is the leader of the Lucavi, but in her absence Hashmal is left to lead the effort to revive her. Ramza runs afoul of the Lucavi by discovering what they are up to, and is forced to fight and defeat the Lucavi one by one. By the time he catches up to Hashmal, however, he is dangerously close to reviving Ultima due to the countless bloodshed needed for the resurrection to work. Ultimately, Hashmal succeeds by committing suicide to fulfill the ritual. Ramza then battles Ultima, who transforms into a giant skeletal monstrosity mid-battle. This is still not enough, however, and Ultima is destroyed, though the resulting explosion devastates the area, and it appears Ramza has perished as well. However, Orran Durai briefly sees him afterward, so it appears Ramza managed to survive the Angel of Blood's demise, although it is up to the player to decide.

Music
"Helldance" ("The Pervert" in the original version) is the Lucavi Boss Battle theme from Final Fantasy Tactics. It begins to play immediately after any Lucavi-possessed character transforms into his Lucavi form, and stops playing right before the defeated Lucavi explodes. The theme is predictably in minor key. It begins slowly and becomes faster partway through only to become slow again just before it repeats. During the slow part, there are four beats to a measure and during the fast part there are only three. It also switches keys twice during the fast part before reverting to its original key. The combination of these irregularities works well for the fact the heroes are in the presence of something unholy whenever it is being played.

Cúchulainn, Belias, Zalera, Adrammelech, Elidibus, and Hashmal all use this theme. Ultima, however, has two themes of her own which are used instead for the battles against her.

Etymology
The Russian word "lukavy" (лукавый) means "deceptive". It is commonly used as a euphemism for the Christian Devil. It is related to the Greek word "lykaugea", which means "twilight".