0 Series

The 0 Series is a mysterious series of weapon unlocked in the Legendary and Vassal Weapons. It is said to be effective against "Those who possess eternity".

Overview
By absorbing a drop of Red Poison, which can be found in a Guardian's base like Sanctuary or the Ancient Labyrinth Library, the 0 series is unlocked. This form of weapon has 0 in every stat with the special effects of "Judge of Reason" and "World Protector". The skill "0" has zero cooldown time and consumes zero SP.

Information to be added later on

History
The Red Poison was first found in the depths of the Ancient Labyrinth Library. After absorbing it into Kizuna's Legendary Hunting Tool, she unlocked a weapon called "0". Later on, she is able to use it to expel the doping powder that the Vanguard of the Wave Seya was using. Realizing that they could use this series of weapon to "repel the connections formed by illegitimate power, the Heroes then test this weapon against the crack in the sky caused by a wave. Almost immediately, the wave started to recede and the time until the next wave was longer than usual.

Returning back to the world he was summoned to, Naofumi started the search for more of the Red Poison to unlock the 0 Series for himself. With the help of Fitoria, he was able to find it at the heart of Sanctuary. He, and all the heroes present unlocked the 0 Series weapon for themselves. The room containing the Red Poison also had murals depicting the Legendary and Vassal Weapons as well as a cat-like entity. According to the mural, the 0 Series is effective against those who "possess eternity" or the self-proclaimed gods. With these weapons, the heroes are supposed to act as "stopgaps" until true help can arrive. Later on, Naofumi unlocked the Dragon King Shield which had the equip bonus called "Beginning of 0".

While in the ancient past, Naofumi and his party encountered a self-proclaimed god during a wave. The self-proclaimed god nicknamed "Cathead" easily overpowered the entire group. However, the Legendary Shield pointed Naofumi to the 0 Series and it skill. Suddenly he was able to block Cathead's attacks. Surprising Cathead, the heroes switched to their 0 Series weapons and killed him.

Trivia

 * Holn hypothesizes that the power to unlock the 0 Series was left behind by God Hunters for future generations.