Legendary Weapons

The Legendary Weapons (伝説武器) are ancient spirits who manifest themselves as weapons and forcibly summon suitable users to resist the the fusion of worlds. The users who wield these weapons are given the title of Legendary Hero.

They are also referred to as the Four Holy Weapons (四聖武器) and the users that wield them as the Holy Heroes, since many regions are formed centering around the weapons. For each Legendary Weapon in a world, there are two Vassal Weapons to assist.

Origins
Each of the legendary weapons were from their own respective worlds. These worlds were fused together as one by the Waves of Calamity, the world of the shield and bow were fused together and the world of the sword and spear were fused together, later fusing together as one, altogether the total fusions of the worlds to three times with a total of four legendary weapons.

The role of the weapons was to fight against their original enemy, the one pulling the strings behind the scenes, seeking to destroy the worlds by fusing them using the waves. The users of the legendary weapons are given the role of saving the world and overcoming the waves after which the user is given a choice of three rewards.
 * 1) Return to their original world, their reward includes three wishes there, for almost anything they could wish for. The spirits can exert some influence over their user's world they operate under. The possibility of bringing back a few people with them is possible, however, that would constitute leaving early.
 * 2) Remain in the world and live out their days there, worshiped as a hero. This is the one that many heroes from the past has chosen.
 * 3) Return once to their own world but retain the right to come back here again.

Summoning & Selection
The legendary weapons are not always able to summon their first choice of hero. In fact, only the Shield Spirit is known for always summoning its first choice of hero. The Sword, Bow, and Spear Spirits often can't summon their first-choice hero in the first place or their hero dies quickly after summoning. If summoning fails, they have to summon backup candidates who have serious character problems. As a reward, these candidates have their deaths corrected.

The legendary weapons are summoned to the response of the waves, appearing in a set of unique weapons, usually four in total. The summoning rituals will also select people from other worlds to wield these weapons; in Naofumi's case, he encountered The Record of the Four Holy Weapons while browsing the library. Once a Legendary Hero is deceased, their weapon will disappear in wait to be summoned again with a new hero. The weapons can be re-summoned if either the current set of waves is vanquished, or the set of weapons is expunged. With each weapon missing, the waves are said to grow stronger.

After a summoned Legendary Hero, there is a chance of another legitimate wielder taking up the weapon. As an example, the Legendary Ofuda was captured by the Third Army after its original wielder was killed. It then summoned Shildina to its world to eventually become its new wielder.

Functionality
The potential of the Legendary Weapons are superior to Vassal Weapons. However, they have more restrictive functions. The main difference is that Legendary Weapons are restricted to protecting their home world while Vassal Weapons are allowed to travel between worlds.

All weapons possess a gem that acts as the functional matrix to activate abilities, this gem persists in every weapon form. Possessors of the weapon upgrade it through adventuring within their respective worlds, with each world having different power metrics.
 * Restrictions


 * Possessors of the Legendary Weapons are unable to gain experience when in close proximity of each other.


 * Possessors may not equip weapons that are not of the same class as the Legendary Weapon itself. If they attempt to handle another weapon, they will be zapped.
 * Possessors cannot remove the Legendary Weapon from their bodies. If they throw it away, it will appear back in their hands
 * Possessors of the Legendary Weapons cannot travel between worlds unless they get express permission from powers such as a Guardian Beast or the spirit of the Legendary or Vassal Weapons.

Curse Series
Legendary Weapons respond to the user's strong negative emotions caused by heavy emotional or physical strain and traumatic events, unlocking the Curse Series variant related to said emotions.

The Curse Series grant powerful effects, stats bonuses, and abilities, but a severe penalty which scales to the severity of the Curse level is applied to the user when the variant is removed or its skills are used. The seven known curse series are wrath, greed, gluttony, pride, lust, envy, and sloth.

Trivia

 * It's not explained why the weapons of Raphtalia's World pick people from Earth as Heroes rather than their own universe. Possibly it may be due to the lack developed will due to the medieval setting.