The Heroes are twelve individuals who exist to save the world when it is faced with the destruction caused by the Waves. They also frequently appear in times of peace, but are not supposed to. There are in total twenty four actual heroes, twelve from Melromarc's world and another twelve from Glass' world, they are divided between the Four Saint Heroes and the Eight Vassel Heroes in both worlds, the former individuals must be summoned from another world(typically a parallel Japan) while the later eight are weaker but can be chosen from both summoned individuals and natives. Each Hero recieves one of the corrosponding weapons, each of which has its own method of strengthening unique unto itself, each hero has the ability to authorise a Class Up beyond the LV.100 cap and can aquire the strongest form of magic, Revelation-Class Magic, which is unique unto them. The Enhancement Methods can be shared by the Heroes, making the resulting weapons far stronger, thus the heroes are at their peak when all twelve are working together, however the weapons from Glass World and Melromarc's are incompatible for whatever reason and cannot share their Enhancement Methods.
The Four Saint Heroes originally all came from four different worlds which were fused over time by the waves into one world, each one originally had two Vassel Heroes serving under them. Both Melromarc's World is a fused form of a world once containing humans, with the Legendary Spear and Sword, and a demi-human world once home to the Legendary Bow and Shield. Glass' world, which also has Four Saint Heroes, is assumed to have gone through a similar process.
Four Saint Heroes
In Melromarc's world the Four Saint Heroes consist of the Legendary Sword, Spear, Bow and Shield's wielders. While the other three weapons are worshipped by Melromarc itself, the shield is loathed by the country for various reasons, mostly for being a recurring ally to the demi-humans, towards whom Melromarc's people show open contempt. These heroes must be summoned from another world, usually a parallel Japan.
Hero of the Sword
The hero chosen to wield the Legendary Sword, primarily noted to be the strongest in attack power. It's Enhancement Method revolves around proficiency, a user can raise the proficiency of a weapon by frequently using it, after which they can even transfer that proficiency to a new weapon when the current one becomes obsolete. Current: Amaki Ren.
Hero of the Spear
The hero chosen by the Legendary Spear. notable for having high attack power and speed, also has forms that can be thrown. The Enhancement Method appears to be Enchanting, where the user can use items and monster drops to imbue the weapons they wield with specific magical properties. Current: Kitamura Motoyasu.
Hero of the Bow
The hero chosen by the Legendary Bow. Capable of long ranged attacks. The current wielder appears to have been chosen partially due to his esper power: Accuracy, which makes it impossible for him to miss unless the projectile is physically obstructed. It's Enhancement Method revolves around using ores to raise the rarity and thus power of the weapons. Current: Kawasumi Itsuki.
Hero of the Shield
The hero chosen by the Legendary Shield. Notably has the highest defence among the weapons by far, easily able to endure attacks from the other weapon users, even when its wielder was at a noticably inferior level. The exact Enhancement Method is unknown, but Naofumi himself relied on unlocking the passive abilities of all of his weapons, thus carrying their benefits over to the other forms, and also on the Growth Corrections of various series, which perfectly suits its user's role as a supporter in battle. Current: Iwatani Naofumi.
Eight Vassel Heroes
Hero of the Fan
The hero chosen by the Legendary Fan. Notable for having techniques which act as a double edged sword. The Fans themselves are hard enough to break swords and appear to generate powerful magical/wind based attacks. Current: Glass