Waves of Calamity

The Waves of Calamity are a mysterious, reoccurring phenomenon that devastates the nearby lands and warrants the summoning of the Legendary Heroes.

True Nature
According to an ancient tome within the Ancient Labyrinth Library, in the universe, there are many different dimensions or "worlds" floating around. Due to their free-floating movement, these worlds very rarely impact each other. If they do so, the border between the worlds may bleed and dimensional cracks in the sky will appear. Monsters will escape through the dimensional cracks and the two worlds will fuse if the "wave" is not repelled. As the fusion occurs, the world that fails at repelling the wave is destroyed. Its sun vanishes and everything turns into a lifeless barren plain which then crumbles away. On the other hand, the opposing world then gains power. It is possible for the heroes to completely repel the wave so neither world is destroyed. This phenomenon is extremely rare and the odds are like two stars in the vastness of space directly hitting each other.

The waves of calamity are the result of this natural phenomenon occurring extremely frequency due to the manipulation of an ancient, all-powerful "World Eater." Through its interference, the worlds have become like balls on a billiards table - hitting each other randomly and often. It is unknown if the world eater is destroying worlds to gain the "bonuses" of doing so or for some other reason.

Confronting a Wave
The Red Hourglass of the Dragon's Era is a vital piece of technology which is intimately tied with the Legendary and Vassal weapons. These dragon hourglasses are scattered across each world in their own respective territory and give the time until the next wave for that territory.

When a wave occurs the Four Holy Heroes and their companions can be summoned directly to the location of the ensuing wave, except in the case of the Guardian Beast waves, which are unique in that the heroes are not meant to fight against them at all. Naofumi also found that adding a leader of another party, say a group of knights, as a member of your own party also transports him and his subordinates to the location of the wave as well.

The Legendary Weapons and Guardian beasts were created to combat this enemy by preventing and repelling the waves. As such, the waves are much less frequent if the Legendary Heroes and Guardian Beasts are allowed to fulfill their duties. With all four Holy Heroes active, the waves occur roughly every month but that quickly increases as heroes are killed. If all of the Legendary Heroes are killed, their world is destroyed instantly. If the guardian beasts are unsealed and able to rampage, the time between waves increase proportional to the amount of life killed. If they are able to complete their work by killing approximately 2/3 of the world's life forms, the waves will never occur again for that world.

The Guardian Beasts
The Guardians Beast are the Spirit Tortoise, Phoenix, Kirin, and Dragon King. These beings have all been sealed away at present and were meant to be an emergency backup to the Heroes. However, through interference of a vanguard of the waves, the Spirit Tortoise woke up far earlier than planned. They cannot be sealed again during the last waves, meaning they must either be destroyed or allowed to fulfill their role as it is no longer possible to simply "survive" the Waves.

Once released they cause immense destruction, they pursue all living things, kill them, and consume their souls. However, their purpose is not malicious, rather it is to confront the waves and save their world. By storing up souls they manage to push back the waves(the gap after the Spirit Tortoise's rampage to the Phoenix's is three months long due to the sheer number of people the former killed, compared to the standard one-month gap) and they can effectively stop the waves in exchange for killing 2/3rds of the world's population.

Role of the Heroes
The heroes actively work to combat the waves when they occur. The Holy Heroes and Vassal Weapon Wielders also act, by their very existence, to keep their world in place and prevent it from merging with the other world. None of the previous generations of the heroes have ever actually managed to defeat the waves, rather they have all just managed to survive them. It is thought that while the Legendary Heroes stay in their world to protect it, the Vassal Heroes are also free to move to the opposing world to destroy it. According the the spirit of the Legendary Shield, it is impossible to defeat the World Eater behind the waves directly with the Legendary Weapons.

The One Behind the Waves
The entity behind waves has not yet been revealed and has only been named as "World Eater"(Naofumi), "Self-proclaimed God" (Old text), "general"(S'yne's sister). The entity had also placed a fail-safe within all reincarnated individuals to prevent them from revealing any information about it in any form. The fail-safe would the destroy the individuals body and soul before a single word.

History
In Raphtalia's World, the four Holy Heroes and the eight Vassal Heroes (two Vassals were made to serve each Hero) came from completely different worlds, which ultimately were destroyed/absorbed into other worlds by the waves. The Bow and Shield worlds and the Sword and Spear worlds were first merged together. Finally, the worlds of the four weapons merged together to create Raphtalia's World. The Bow Hero and Shield Hero came from the world where the Demi-Humans/Beastmen originated while the Spear and Sword Heroes came from the world where humans lived. The Bow Hero managed to make himself well received by the humans while the Shield Hero remained a figure of contempt for them up to the time where Shield Hero Naofumi Iwatani was summoned.

In a similar vein, Glass' world also has Four Holy Heroes and Eight Vassal Heroes separate from those of Melromarc, they also have three races, Humans, Demi-Humans (in their case, dwarves, elves and the like, as opposed to the Beastmen and animal-like Demi-humans of Raphtalia's world), Crystal people, and Ghost kin, all of whom are assumed to have immigrated from other worlds during past waves.

The strongest known worlds have four heroes. The organization behind the waves considers any world with eight Holy Heroes to be a significant threat and thus does their best to prevent it from happening.

Known Waves
The waves are not a recent event and have been occurring since ancient history. However, due to the efforts of the vanguards of the waves, much of that history has been destroyed. The four Holy Heroes Naofumi, Motoyasu, Itsuki, and Ren are summoned just after the first wave of its wave period. The waves listed below are the main ones seen in the story, however, several other waves are noted to occur over the globe during this period which are handled frequently by other parties.

Pre-Guardian Beast Waves
The waves taking place before the four Guardian Beasts were released to stop the wave. These waves are typical, with the sky splitting as two worlds collide and monsters coming out. They have a stable month gap between their onsets and the monsters are weak enough to be handled by a proper military response, even some adventurers are shown to be able to hold their own against monsters of these waves.

First Wave
Struck at Lurolona Village in Melromarc, this Wave killed Eclair's father, Raphtalia's mother and father, and rendered several demi-humans homeless and/or at the mercy of slavers, this was not helped by the King of Melromarc's hate of demi-humans and the queen's unfortunately timed absence. This event led to the king summoning the Four Holy Heroes.

Enemies

 * Cerberus (Boss)
 * Two-Headed Black Dog

Second Wave
Struck near a small town in Melromarc. The casualties were severely reduced due to the quick response that the knights could provide due to the distance from the Castle Town being short and the heroes Motoyasu, Itsuki, and Ren managed to easily slay the Chimera acting as the boss. Meanwhile, the Shield Hero Naofumi directly protected the nearby town and saved countless lives in the process but would go unrewarded by Melromarc's King for his contribution due to favouritism.

Enemies

 * Chimera (Boss)
 * Inter-Dimensional Zombie
 * Inter-Dimensional Locust

Third Wave
The third wave occurred near a number of villages in Melromarc's northern region. During this wave, the Shield Hero Naofumi managed to bring several knights with him at the time of teleportation, which was good because the distance from Melromarc's Castle Town meant it would take a day and a half for the knights to arrive normally. Together with the knights and some adventurers, as well as a certain old woman who happened to be a retired Level 100 adventurer, Naofumi managed to defend these towns. After three hours, however, the Wave still hadn't ended and Naofumi was forced to investigate why the other three heroes hadn't stopped it yet and he finds them defeated by Glass, who herself had already killed the wave's boss. Naofumi engages and defeats Glass together with his party, forcing her to retreat while warning him not to believe the waves are just a natural disaster.

Glass later notes her intention was to destroy Melromarc's world by killing off its heroes in order to save her own world, something Naofumi notes he can't argue with as he'd likely have done the same thing in her position.

Enemies

 * Soul Eater (Boss)
 * Shadow Assault Goblin
 * Shadow Assault Lizardman
 * Skull Captain
 * Kraken
 * Ghost Ship

Fourth Wave
The fourth wave occurred in the Cal Mira Archipelago area. While exploring, Naofumi, Raphtalia and Filo find an underwater temple with an hourglass. The glass noted that there was only about two days until the next wave in that area. Naofumi then got Queen Melromarc and her forces to come fight the wave. Ren, Itsuki and Motoyasu hardly did any damage while L'Arc and Therese were the ones who were actually able to defeat the final boss. However, once the boss was defeated, L'Arc and Therese tried to kill Naofumi as Glass showed up. Due to quick thinking from Rishia and Queen Melromarc, they were able to intoxicate Glass with rucolu fruit. Finally, timer for the ending of the wave appears and the three other-worlders retreated.

Enemies

 * Inter-Dimensional Whale (Boss)
 * Inter-Dimensional Sahuagin Shadow

Four Guardian Beast Waves
The Four Guardian Beast's waves are distinct from those before for a number of reasons. The Beast's primary purpose is, in fact, to suppress the Waves and protect the world by killing 2/3rd's of the population on it and absorbing their souls. They aren't meant to be fought, thus the Four Heroes aren't summoned to their location and aren't supposed to fight them at all. They can ultimately stop the waves if left to do their job, but will, as mentioned above, accomplish it by killing off millions of living beings. The more they kill during their active periods the more time lasts until the next wave, for example, the Spirit Tortoise managed to kill thousands of people during its rampage and as a result the Phoenix's wave occurred three full months later, however, the Phoenix didn't kill many people by comparison and this caused the wave of Kirin to occur only three days later.

Spirit Tortoise Wave
This wave occurs when Kyo improperly unseals the Spirit Tortoise, effectively skipping any waves that should've occurred prior to this one and pushing this one forward. This wave was indicated to be the same difficulty level as what would have been the seventh wave. Naofumi, together with an allied force led by Melromarc's Queen, confront the Spirit Tortoise in a bid to seal it anew but find that it is impossible to seal the beast. Naofumi interprets the messages of a previous hero, one named Keichi who helped seal the turtle to start with, that the turtle can only be killed by destroying both its head and heart at the same time, which he proceeds to do just as it started storming the Castle Town. This incident itself took roughly a full month to resolve.

Enemies

 * Spirit Tortoise (Boss)
 * Spirit Tortoise Familiars
 * Demon Bat
 * Mimic Type Familiar

Phoenix Bird Wave
The Phoenix Bird Wave occurs 3 and a half months after the Spirit Tortoise incident. The allied forces and Four Heroes mounted a massive force to confront Phoenix, who revives in the form of two Phoenix that must be simultaneously slain (should one go down before the other, it'll self destruct and both will revive from its ashes). Upon checking the seal before the revival, it is found that the area had been tampered with and a "hard-mode" fight had been unlocked. The allied forces nearly defeated the two Phoenix birds without suffering heavy losses, but the sudden interruption of a certain individual killed one of the Phoenix birds too early and triggered the second to self-destruct, killing a large number of the allied force, including Atla. Atla's sacrifice allows Fohl to awaken the Seven Star Gauntlets and with her dying words, she encourages Naofumi to unlock the Shield of Compassion, which allows him to vastly increase the power of all slaves, demi-humans, and companions forming the allied force with sudden growth corrections. The allied forces swiftly slay both Phoenix birds with this newfound power and begin hunting down the one who interrupted and caused the deaths of so many of their comrades.

Enemies

 * Phoenix (x2; Boss)
 * Phoenix Familiars

Kirin Wave
The Kirin was summoned only a few mere hours after the Phoenix birds in the kingdom of Faubrey and comprises Kirin's unsealing. This wave is resolved by Takt and his army soon after. Naofumi theorizes that the reason this wave struck so fast is either due to the swiftness of the Phoenix's suppression preventing casualties, or Takt's senseless murdering of four seven Star Heroes sometime prior to the Phoenix's revival.

The blue hourglass summoned by the Spirit Tortoise disappears after Kirin's demise and was replaced with the red hourglass used for typical waves.

Enemies
Kirin (Boss)

Post Guardian Beast Waves
After the first three guardian beasts had been defeated, the regular waves had begun again. However, this time the various countries and heroes were united to fight against them.

Dragon Emperor Wave
The final guardian beast, the Dragon Emperor, has not yet been summoned for either Raphtalia's and Glass' world. However, it seems that it has a different summoning condition than the other three guardian beasts relating to the Dragon Emperor fragment. After Gaelion obtained several fragments from Leludia of Takt's forces, he learned the requirements to summon it.

Trivia

 * The four Holy Heroes only initially had access to Melromarc's dragon hourglass and thus were ignorant of the other waves around the world until Fitoria alerted Naofumi.