Vanguards of the Waves

Reincarnated Individuals are people who were reborn into the world of heroes and they retain their memories of their previous life. They had been reincarnated by a the "Beings Who Call Themselves Gods", otherwise known as Fake Gods.

Personality
All of the reincarnated individuals have common character traits. They are all prideful, arrogant and self-proclaimed geniuses. All of them think of this world to be games and doesn't bother about life inhabiting the world. They don't really care for the wave and are trying to fulfill their own selfish delusional desires. They mostly refused to listen to others opinion or reasons and only tries for their own satisfaction, Such as, forming a harem, being king, and calling themselves the heroes.

They are overconfident and try to stand out as much as possible while some choose to hide their power. As Naofumi stated, most of them are otaku or gamers in their original world and try to outshine others in this world. They believe in their self-righteousness, as they are chosen by the Fake Gods.

They form an antithesis to the Heroes, as they directly work for the force that is trying to destroy the world and work to sabotage or kill the Heroes at whatever time they can. They cause chaos, confusion and mess things up with their twisted or otherworldly logic. In times of their demise, all of them proclaims that they will return or again reincarnate or demand a redo from someone unknown. They are mostly responsible for the loss of many important information and also the loss of order in the world.

Abilities

 * Legendary Weapon Stealing Ability: Processed by Takt, this ability allows the Reincarnator to steal the physical forms of the legendary weapons. The ability can only steal the Legendary Weapons' physical forms and not take control of their inner energy. As seen with the Vassal Projectile being able to give Rishia it's energy form. The thief can't get full access to the power up methods. For example Takt only got magic at level 3 with the Vassal Staff's power up method when it can go to level 10. The Legendary Weapon's stats and power up methods don't stack with each other as well either, since no one is supposed to be the hero of more than one Legendary Weapon at a time.
 * Inter-Dimensional Storage: This ability allows the Reincarnator to store items in a personal dimensional space. The Reincarnator who stole the Holy Cards had this ability, showing it off when he pulled a longsword out of thin air.
 * Barrier Ability: Used by the Reincarnator only known by "The Enemy of the Week". Forms incredibly tough barriers. They can be used offensively to crush beings inside.
 * Status Menu Viewing: Used by the Reincarnator nicknamed "Ren #2" by Naofumi, this ability allows the Reincarnator to see other's level and stats.
 * Soul Permanency: After dying, those with this ability survive as free roaming souls. In this state they can talk and attack people and remain unseen by normal physical beings unless certain magic or Legendary Weapon forms such as a Soul Eater form are used. They are able to jump into a body that doesn't have a soul like a homunculus or a person with a hole in their soul like Sildeena. Free roaming souls are vulnerable to soul eating monsters and weapons meant to attack the incorporeal and can be finally killed by them. Every Reincarnator has this ability and people from Hero Worlds that ally with them can be given this ability.

History
Elrasla Grilaroc of Hengen Musou stated that "Geniuses were the apostles of social growth and decay." One such individual was under the impression that he was the one worthy of ruling the world, and Musou teachings forbid such ways of thought and so he ended Hengen Musou teaching by starting an internal discord. This eventually led to the downfall of the technique and lost in time, except for Granny (who later pass it on to Naofumi's comrades). After facing Takt, Naofumi and other heroes come to the conclusion that they were not geniuses but was actually reincarnating people from another world with their knowledge intact from their world.

After his weapons was stolen away, Naofumi was in the Legendary Weapon Spirit realm were the Spirits reveal that an endless enemy sends the Reincarnators to act as wave vanguards. After listening to the story, Naofumi pieces together the information of the Queen, Granny, and Legendary Weapon Spirits and concluded that these Reincarnated one are chosen by the one causing this Waves to act as enforcers in the destruction of the Hero worlds.

Like Hengen Musou, many techniques, technology and other means that give the advantage to fight waves used by the past heroes disappeared in the passage of time. Naofumi predicts that the Fake Gods use these Reincarnated people from another world to take away the means to fight against the Wave and to make sure these powers would fade away one day. Even if these individuals acted on their own ideas and belief, they succeeded in fulfilling what the Fake Gods wanted.

Reincarnators have destroyed the knowledge of the way to fight Phoenix and the Spirit Tortoise, the means to break the Level 100 Cap, the destruction of the Hengen Musou School and various pieces of other information over the ages. As this information of great value, cannot disappear in a natural way.

In Glass' world was also left with information on what the wave was, but everything else was lost over time. Naofumi find this ancient information on Glass' world regarding killing the other world holy heroes to prolong their world to be nonsense and suspect it to be fabricated, as one of the holy weapon (Hunting Hero) in her world lacked fighting ability much like himself, if their concept were true, all the heroes need to excel in combat and also because their world's vassal weapons assisted him and his party to take down Kyo  One vassal weapon, Katana, even choose Raphtalia as its wielder and went to Raphtalia's own world which all made Naofumi doubt the ancient theories of Glass' world.

The differences between the Reincarnators' actions and number of between worlds has been theorized due to how quickly time flows in the different worlds. While Raphtalia's world was sabotaged, Glass's world which experiences time about twice as fast as Raphtalia's world, was left alone for the most part.

Summary
It's been noted that there were rare geniuses who have appeared throughout history in both Melromarc's world and also Glass' World. Naofumi finds these geniuses to be just a Reincarnated Individuals retaining their previous world's knowledge

Naofumi names those who mediates reincarnations individual as "Beings Who Call Themselves God", based on the warning recieved by S'yne's Sister. He clarifies that it claims that the supposed Gods are not really divine. According to the novels Naofumi and the other heroes read, If someone were to die in a tragic accident, he would call out to them. To those who faced such misfortune, he would say that you died an unfortunate death, I will give you life once more in another world?. It is nothing but a tempt. Since they're dead, there's no way they can refuse. Even If they decline, god will tempt by words of developed a liking for them, so give them a cheat. In away forcing them to agree with either way. There's also the possibility of forceful reincarnation without any interaction. Knowing the Fake Gods were the ones who reincarnated them, they feel special and develop a superiority complex and doing things of their own self-righteousness. If the reincarnated one was a gamer than he sees this as nothing but a game. They are just a playing piece that cuts off the lineage that aids the heroes.

In Glass' world, they have had an even more adverse influence but rather in the opposite direction, they have instead increased knowledge on the Heroes' weapons and mission but warped it to serve their goals. Two such individuals are known, Trash #2, as Naofumi calls him, and Kyo. The former formed a harem, introduced new technology and wanted to become the Vassal Katana's master, however, he failed and the weapon chose Raphtalia instead. The latter was a significantly greater threat as he worsened the Spirit Tortoise rampage, and then stole the Holy Beast's power when he was defeated thus having a massive negative impact on Raphtalia's world before he returned to his own. This sin was bad enough that his own Vassal Weapon, The Book essentially called out to Glass' group to execute him and when even that wasn't enough Naofumi, who cannot normally cross worlds as he is a Holy Hero, was granted an exception in order to exterminate him.

The country of Faubley was completely taken over by one reincarnator named Takt, who then attempted to take over the entire world and use his power to steal the Legendary Weapons from their rightful wielders. Tact appeared to be under the impression he was actually saving the world, but because of his sheer selfishness, arrogance and stupidity was, in fact, leading directly to its impending destruction. He was defeated by the Heroes, Naofumi, Fohl, Trash, Ren and their comrades, and the weapons he'd stolen were then taken by other Reincarnator forces. This happened because of the Legendary Weapon Stealing Accessories Takt had atached to his 5 Vassal Weapons.

He was then promptly executed and his soul consumed by a soul eater. Trash and Naofumi then set about warning the countries of the world to keep an eye out for anyone who matches the description of a reincarnated individual and keep an eye on them to prevent another danger.

In Glass' world, the situation became much worse due to them not noticing the Reincarnators in time. One reincarnator tricked several heroes into distrusting their comrades and killing each other. As many as two are known, one of them being Ciel, who believes the world is a game and that by killing his comrades and instead of aiding in the Wave's advance he is letting the game install "Updates". Both reincarnators are noted to be in control of two large kingdoms. Eventually, Ciel passes through the Wave and enters Melromarc's world, calling it "A new world aided by the Goddess' Update," and tries to force the Wave open to get in. He uses his barrier ability to hold off the heroes who desperately attempt to stop him from his goal. Their shout of wanting to stop the wave and their reason of it being the world fusing together resulting in not even a blade of grass to grow to feel on their deaf ears. The heroes fail, causing the goddess, Medea Pideth Machina, to descend upon the world. After Medea promptly kills Motoyasu, Naofumi, and Ren, she sends her army of reincarnated to destroy what remains, allowing them to pillage and assault Melromarc for the sheer fun of it while all of them are still somehow under the impression that it's all a game, despite her openly admitting she intends to destroy the world, with them in it, when she's done.

Trash #2
A Reincarnated Individual from the Light Novels. He had a sizeable harem and was an inventor who created clones of the Sacred Beast, the White Tiger, and also found ways to prevent the Heroes from warping away to safety. He wanted to get the Vassel Katana but became envious and wrathful when Raphtalia got it instead. He is backed by his nation in hunting Raphtalia down but he ultimately gets himself killed when Raphtalia subdues him in a way that if he moved before receiving healing magic he would die, this tactic was only meant to allow Raphtalia's group to escape but Trash#2 ignored the warning and thus got himself killed.

Kyo
A reincarnated individual first introduced in the Light Novels then added into the Web Novel through the Spear Reprise Web Novel (these chapters came out after volume 7 came out in Japan). Like most of them, he is a "genius inventor," while he is evidently quite smart and competent at strategy he is insufferably smug about it to the point he thinks he's much more so than he really is. Kyo killed Albert and turned him into a puppet before going out to take control of the Spirit Tortoise. He took control of the Spirit Turtle and sent it on a rampage and used it as an energy collecting medium fueled from every living being it killed under his control. After Naofumi killed the Spirit Tortoise, Kyo took the energy he had and fled back to Glass' world. When the Heroes chased after him, Kyo flung Naofumi and Rishia, the people he hates the most and a Holy Hero, into the Inter-Dimensional Prison that Holy Heroes can't escape from. Kyo took control of the his home country of the Vassal Book and the countries of the Vassal Mirror and Vassal Katana. After Trash #2 died he took control of his soul and manipulated his harem after he took control of the Vassal Katana country. He lead the 3 nations into a war with L'Arc's country but ultimately being tracked down and defeated at his secret mansion by the Heroes. Raph-chan pointed out his soul which appeared to be that of the middle-aged man. Raphtalia sliced Kyo's soul in half with her Katana's Soul Eater form and Rishia threw an ofuda that contained Soul Eaters which went out and devoured the rest of his soul.

Albert
Albert was a reincarnator. He wasn't revealed to be one earlier due to Kyo killing him before the Reincarnators of Glass's world started showing their true personalities. He never used the Vassal Mirror's Cooking based power up method due to it possibly making his harem fat. He did not corporate with Glass and the other real Heroes before his death at the hands of Kyo. It is very likely Kyo killed Albert before he went to take over the Spirit Tortoise. He wasn't around in the country of the Vassal Mirror when Naofumi, Kizuna, and Rishia escaped the Inter-Dimensional Prison, even during the Legendary Hero teleportation replication event that had a lot of security. Events in the WN and Spear Reprise WN (that were written after Volume 7 was released in Japan) reveal more evidence that he was killed by Kyo before the Spirit Tortoise incident.

Unnamed Reincarnator Scouts
According to S'yne two of them helped to destroy her world by killing the holy weapon wielders. Now they were aiming to kill Naofumi and other holy weapon wielders of the world. When Naofumi tried to reason with them, they just that they wanted to prove that their world is the strongest and also they kill to get bonus and powers for themselves. Disgusted with them, Naofumi and his team killed them but their souls kept surviving and were brought back to their world. From there they got new bodies and kept getting past the Spirit Tortoise's wave barrier. Finally, after them being killed for the second time, the rampant use of curse series skills prevent their souls from being warped back to their world, and Raph-chan pointed out their souls to Raphtalia who destroyed them with her Vassal Katana's Soul Eater weapon form.

Takt Arusahorun Faubrey
A Reincarnated Individual is given the power to steal Legendary Weapons by the Fake Gods. He acts primarily on the belief that he's saving the world, when he's, in fact, aiding in its destruction. He is over Lv. 350 and has stolen five of the Vassal Weapons by the time he first appears but ultimately, since he's not actually a hero himself, his power is far inferior to the real Heroes once they get their bearings down and he is promptly defeated. Takt and his harem and forces were all captured by the Heroes and their allies, and they forced Takt to watch his harem and his sister be executed in many different ways if he didn't reveal who gave him his Legendary Weapon Stealing Ability. Takt was furious at this because this meant he couldn't have his harem again if he reincarnated. It's also revealed that Takt's parents are already dead (the Shin Spear Reprise WN reveals Takt was the one to kill his father, meaning that in the LN he killed both of his parents). After getting tortured by a few defecting Malty like women, he demanded a redo to an unknown entity, so he would again reborn in this world to avenge himself. The heroes revealed that they have been Soul Vacummers to suck up and eat all the executes' souls and threatened to have his soul sucked if he didn't give them the information they wanted. Realizing he would actually be killed permanently, he was about to tell them what he knew but his head exploded and his soul tore itself to shreds.

"Former Friend"
This Reincarnator was part of Kizuna's friend group and possesed the Legendary Weapon Stealing Ability. After Miyaji and the Harpoon Reincarnator killed the other 3 Holy Heroes of Glass's world, this guy attacked and stole L'Arc's Vassal Scythe during a meeting between countries disguising what to do about the two apparent rogue Vassal Heroes. He was killed after Glass turned him into a bloody mist after receiving a Liberation Aura X from Naofumi and the Scythe returned to L'Arc. The Mark 1 Legendary Weapon Stealing Accessory the Reincarnator put onto the Scythe shattered as it returned to it's true hero like with Rishia and the Vassal Projectile. It is unknown if this guy and the "Scythe Vassal Reincarnator" from the WN are the same person.

"Enemy of the Week"
This Reincarnator posesses the Barrier Ability similar to Ciel from the WN, but they are not confirmed to be the same person.

"The Two Sneaks"
These two Reincarnators tried to sneak into the Level 100 Cap Breaking ceremony. After the failed attack by S'yne's Sister, "Enemy of the Week" and Lesty, they were captured by the Heroes. Raphtalia stabbed one with her Katana's Soul Eater form and pulled out his soul, showing it's appearance as someone from a world like Naofumi's or the other Japanese Heroes. Both their souls were eaten by the Demon Dragon.

Reincarnator Like People
There are non reincarnated individuals of the Hero Worlds that have suspiciously done much work for the goals for the Reincarnators and their masters. So far the only two people that fit under this category are Malty and Makina.