Genjuu

The Genjuu are mighty elemental beasts that inhabit the respective eight regions of Ankoku Nui. According to Jikanmu, they either turned evil and caused the planet's decay, or became hostile as a direct consequence of the phenomena that occur in their domains. Both these assumptions are false, as Scryptorek made them evil after devastating the planet. Because Scryptorek made himself undetectable to the Genjuu back when he was still ruling over the humans of Ankoku Nui, they turned their attention to human inhabited areas that routinely used Mako Energy, the second biggest threat to the planet's ecosystem. This allowed Dai-Shinra to paint the beasts in an inherently hostile light, and prompted them to create the Rykyrpuds.

All of them "returned to the planet" upon their deaths, and given Vakama and Aerith's statements that life is finally returning to Ankoku Nui, it is quite possible that the Genjuu will return to life as their originally benevolent selves(in the Liche's case, it would be revived as the human it once was before experimentation).
 * Efreet (イフリート Ifurīto, Ifrit) - the red lion/djinn Genjuu of Ta-Aka. It was slain by Cloud Strife.
 * Bismarck (ビスマルク Bisumaruku) - the blue whale Genjuu of Ga-Ao. It was slain by Vakama.
 * Valefar (ヴァルファーレ Varufāre) - the green falcon Genjuu of Le-Mido. It was slain by Squall Leonheart.
 * Midgardsormr (ミドガルズオルム Midogaruzuorumu) - the brown/orange cobra Genjuu of Po-Kassho. It was slain by Jikanmu.
 * Kujata (クジャタ Kujata) - the black/grey bull Genjuu of Onu-Kuro. It was slain by Riona Heartilly.
 * Fenrir (フェンリル Fenriru) - the white wolf Genjuu of Ko-Shiro. It was slain by Matau and Rinoa.
 * Ixion (イクシオン Ikushion) - the yellow horse Genjuu of Ina-Kiiro. It was slain by Whenua.
 * Liche (リッチ Ritchi) - the violet undead Genjuu of Do-Mura, the result of Scryptorek performing human experiments on the last survivor of a revolt led against him, which he turned into a Makonoid; thus it is not really a Genjuu. It was slain by Yuna and Rinoa.
 * Kardahamut (カルダアムット Karudahamuto) - An ultra-powerful Genju created by Scryptorek, resembling a cross between Bahamut and the Kardas Dragon. It was slain by Cloud and Squall.

Etymology
Genjuu (幻獣) means "phantom beast" in japanese.

The Genjuu are all named after and based upon (mostly) summon creatures from the Final Fantasy series.

Trivia

 * Efreet is the only Genjuu named after one of the most recurring summoned creatures, and the only Genjuu to appear in both Bionic Fantasy and it's upcoming prequel.
 * Some of the Genjuu have cultural aspects to their designs, such as Midgardsormr being themed after an Egyptian pharaoh, and Valefar being adorned with African tribal accessories.
 * Six of the Genju are fought and defeated in the same order as Lhikan giving the Toa stones to the Toa Metru as shown in BIONICLE 2, with Ixion and the Liche following after.
 * The role they play as planet protectors-turned enemies of the protagonists is similar to the WEAPON creatures from Final Fantasy VII.
 * The Liche is the only Genjuu not based on an animal, and whose Final Fantasy namesake wasn't a summoned creature to begin with, but rather one of the Four Elemental Fiends of Chaos from the first game.
 * However, it's appearance has more resemblance to a cross between Jagi, from Fist of the North Star, and another Liche, hailing from the video game Gauntlet: Dark Legacy.