Guardian Beasts

Guardians Beasts are legendary beasts that are meant to protect their world from the waves.

Overview
The Guardians Beasts are a safety feature of certain worlds against the waves. They are meant to act as a last defence in case the Legendary Heroes are either not powerful enough or unwilling to defend against the waves. However, protection from the guardian beasts come with a great cost. In order to fully protect a world from the waves, the guardian beasts must kill and collect the souls of about 2/3 of life in their world. They then use these souls to power a barrier to keep other worlds away. Due to their terrible cost and destructive power, heroes from Raphtalia's and Glass' Worlds have elected to either seal away or kill the beasts. The amount of life that a guardian beast kills is proportional to the length of time that world is protected from future waves.

Guardian Beasts
The Guardian Beasts of Raphtalia's World and Glass' World correlate to the four benevolent animals of Japanese and Chinese folklore respectively. They are the Spirit Tortoise, the Phoenix, Kirin, and the Dragon King. As of the heroes' second expedition into Glass' World the first three guardian beasts of both worlds have been defeated. However, the final guardian beast has yet to be summoned.

Spirit Tortoise
The Spirit Tortoise is the first guardian beast and is large enough to hold a nation on it's back. It releases infectious cells which can enslave nearby living creatures into becoming the Spirit Tortoise's familiars. In the addition to the giant swarm of familiars, the Spirit Tortoise is capable of a devastating beam attack. The equivalent to the Spirit Tortoise in Glass' World is the Black Turtle.

Phoenix
The Phoenix is the second guardian beast and is actually a twin pair of flaming birds - one specializing in magic, and one specializing in physical attacks. If one bird is defeated, it is capable of unleashing a terrible explosion and then reviving itself as long as the other bird is still living. The equivalent to the Phoenix in Glass' World is the Vermilion Bird.

Kirin
The Kirin is the third guardian beast and consists of a pair of tiger-dragon-like creatures. Not much is known about the Kirin as historical records on the guardian beasts were destroyed. The equivalent to Kirin in Glass' World is the White Tiger which specializes in wind magic.

Dragon King
The Dragon King is the fourth and final guardian beast. Not much is known about this final guardian beast except that it may have some connection to Dragon Emperor fragments divided by different Dragon Emperors and has a different summoning process. The equivalent to the Dragon King in Glass' World is the Azure Dragon.

Volume 6
The first sign of the Guardian Beasts appear when the Spirit Tortoise's familiars start attacking Raphtalia's world to create more familiars. The heroes eventually find through some sparse ancient documents describing the Spirit Tortoise. The Holy Bow Hero, Sword Hero, and Spear Hero fight the Spirit Tortoise but are quickly defeated. Multiple countries, including Melromarc, join an alliance to defeat the Spirit Tortoise. Together, they chop off its head and celebrate its defeat.

Volume 7
Ost, the human familiar representing the Spirit Tortoise contacts Naofumi and warns him that the Spirit Tortoise has not been defeated. As she predicted, the Spirit Tortoise revived itself with a new head and a wicked new form. The heroes fight the Spirit Tortoise and eventually make their way inside with the help of Fitoria. In unison, they destroy the head and heart which defeats the Spirit Tortoise for good. Travelling deeper into the Spirit Tortoise, they find the one responsible for improperly unsealing and controlling the Spirit Tortoise - Kyo. They fight and Kyo eventually teleports to his own world with the energy that the Spirit Tortoise created with the souls of the people it killed.

Volume 9
Naofumi and his group defeat Kyo and return the Spirit Tortoise energy to his world where it gives three and a half months until the next "wave" - the Phoenix.

Volume 15
After a long preparation, the heroes and various kingdoms prepare to fight against the Phoenix. However, it seems that someone had interfered with the unsealing process again and unlocked a "hard-mode" fight with the Phoenix. However, with the forces unified, they successfully engage with the two birds. As they are about to be defeated, one of them is killed by an unknown attacker, far off in the distance, which causes it to undergo an explosive revival. Many people, including Atla, are killed but after a second go, the united forces are able to defeat the twin Phoenix birds.

Volume 16
Naofumi receives word from Queen Melromarc that soon after the Phoenix was defeated, Kirin was unsealed near Faubrey. However, the Vassal Whip Hero and his companions quickly defeated it.

Trivia

 * Each guardian beast corresponds to one of the elite demi-human races of Siltvelt. The races corresponding to the Spirit Tortoise, Phoenix, Kirin, and Dragon King are the Genmu, Shusaku, Hakuko, and Aotatsu respectively. However, there is no direct relation between the two groups.
 * The weapons created out of Guardian Beast material have excellent stats and bonuses, however they often require high stats or levels to use.