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 in time. 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 with extreme frequency due to the manipulation of an ancient, all-powerful entity known only as the "World Eater". Through its interference, the worlds have become like balls on a billiards table - hitting each other randomly and often. During Nafoumi's travel to Glass's World, He witnessed Kyo able to summon the Wave, which confused the Heroes, but confirmed that the Waves are triggered by some unknown enemies. It is unknown for whichever reason the World Eater is destroying worlds, whether to gain the "bonuses" of doing so or for some other motive.

During Nafoumi's time travel to Mamour's timeline, Nafoumi and the villagers noticed the landscape to be oddly familiar and unfamiliar at the same time. During night, Melty and Raphtalia were able to identify a few constellations but some others were missing or different, this made Nafoumi to conclude that rather than worlds as previously though, it might be the universe that were merging.

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 territories, and display the remaining time until the next Wave will usher 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 directly.

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 if 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 increases proportionally 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 cease permanently 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 was awakened 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 by pursuing and killing all living things and consuming their souls. However, their purpose is not malevolent, 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 sacrificing 2/3 of the world's population.

Role of the Heroes
The Heroes actively work to combat the Waves when and where 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 other worlds. None of the previous generations of the Heroes have ever actually managed to permanently defeat the Waves, rather they have all just managed to survive them. It is thought that while the Legendary Heroes must obligatorily stay in their world to protect it, the Vassal Heroes are allowed to move to any opposing worlds and destroy them. According to the spirit of the Legendary Shield, it is impossible to defeat the "World Eater" behind the Waves directly with the Legendary Weapons alone.

Who is the "World Eater" behind the Waves?
The entity behind the Waves has not yet been revealed and has only been referred to as "World Eater" (by Naofumi), "Self-proclaimed God" (via old texts), "General" (by S'yne's sister). The entity had also placed within all of its reincarnated individuals a kind of "fail-safe" which entirely erases the individual from existence (by destroying their bodies and souls) if they ever try to reveal any minimal information about the Waves or the entity itself.

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 and Shield Heroes came from a 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 separated 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 anything in its power to prevent it from happening.

Waves in Raphtalia's World
The Waves are not a recent event, as they 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.

Waves before the Four Guardian Beasts
These specific Waves took place before the four Guardian Beasts were released to stop them. 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 Seaetto's father, Raphtalia's both and parents, and rendered several demi-humans homeless and/or at the mercy of slavers - this situation was further worsened by the current Melromarc King's hate of demi-humans and the Queen's unfortunately timed absence. This event led to the King summoning the Four Holy Heroes by himself, which almost caused a world-wide war of all nations against Melromarc.


 * 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 short distance from the Castle Town and the Heroes Motoyasu, Itsuki, and Ren managing 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 and connected to Glass' World. During this Wave, the Shield Hero Naofumi managed to bring several Knights with him at the time of teleportation - this later proved a good decision because of the long distance from Melromarc's Castle Town (around 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
 * Glass

Fourth Wave
The fourth Wave occurred in the Cal Mira Archipelago area and is the second Wave to connect to Glass' World. While exploring the tropical landscape during their off-work day, Naofumi, Raphtalia and Filo found an underwater temple of red bricks whose inside emitted a distinctive glow - it was a Dragon Hourglass, which signalled only two days before the incoming Wave. Naofumi then got Queen Mirellia 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 truly defeated the Wave 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 Ivyred and Queen Mirellia, they were able to intoxicate Glass with rucolu fruit juice and make her unable to keep fighting. Finally, the timer for the ending of the Wave appears and the three otherworlders retreated.


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

Waves during the Four Guardian Beasts
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 2/3 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 the Beasts are 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 longer will be the time gaps between Wave. For example, the Spirit Tortoise managed to kill thousands of people during its rampage, thus resulting in a 3-month gap until the Phoenix's Wave occurred; however, the Phoenix didn't kill many people by comparison, thus causing the Kirin's Wave to strike 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 eventually found out that it is impossible to re-seal the Beast. Naofumi interprets the messages of a previous Hero - one named Keichi, who helped seal the Tortoise ages ago - explaining that the Tortoise can only be truly 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 Phoenixes that must be simultaneously slain - should one go down individually, the remaining one self-destructs 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, resulting in a large number of the allied force, including Atla, being readily slaughtered by the birds. 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 the battle and caused the deaths of so many of their comrades.


 * Enemies
 * Phoenix (x2; Boss)
 * Phoenix Familiars

Kirin Wave
The Kirin Wave happened in the Faubrey kingdom, comprised by Kirin's unsealing, only a few mere hours after the Phoenix birds were effectively destroyed. 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 regular red Hourglass used to display the remaining time before the typical Waves.


 * Enemies
 * Kirin (Boss)

Waves after the Four Guardian Beasts
After the first three Guardian Beasts - Tortoise, Phoenix and Kirin - 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.

First Joint Wave
This is the first Wave in which the Heroes from Raphtalia's World participated, however Glass' World has seen many Waves before this one. The Wave occurred shortly after Naofumi's and Kizuna's parties reunited after being separated by Kyo Ethnina. The monsters coming out of this Wave were based on Hindi mythology.


 * Enemies
 * Inter-dimensional Ganesha Shadow
 * Inter-dimensional Garuda Shadow
 * Inter-dimensional Demon Elephant (boss)

Second Joint Wave
This Wave, which had occurred during Naofumi's second trip to Glass' World, happened to be between Glass's and Raphtalia's Worlds so anyone who had levelled-up in both worlds had their levels combined. As a result, this Wave was quickly defeated. The Heroes then used the Wave to their advantage to communicate between the two worlds.

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.
 * In the spin-off series, Motoyasu and Naofumi joined forces to fight a Wave in Siltvelt during the fourth loop. They fought mainly Japanese-style demons and monsters with an enormous bald-headed giant-like Daidarabochi as the Wave boss.