Miasma

Miasma (瘴気) is a highly corrosive and poisonous gaseous dark purple mist that originates from Cracks in Mass for the Dead.

Overview
A mist that springs from the depths of the abyss of Cracks. It has a corrupting effect, causing animals and plants to go wild, creating Contaminated Beasts. Even the smallest particles that are invisible can still have an effect. Those who have some power in the New World are not totally immune to its corruption, though the level of tolerance depends on the individual.

The gas coincides when a Crack spews out Chaos Beasts at regular intervals. The substance is only dissipated once all the Chaos Beasts are defeated. However the contaminants contained within the miasma have been shown to not just affect fauna and living things, have some long-term effects on local flora and the earth, creating bizarre creatures.

Trivia

 * However, there are no cases where the people of the Great Tomb of Nazarick have become violent, including the protagonist who has no combat ability. Later on it is elaborated by Enhela Read Gahi who possesses complete control over all the Cracks in the New World that the Crack located in the Throne Room is unique as it is an independent Crack which he has not direct control over, and may be responsible for the NPCs immunity.
 * No cure for the miasma exists so far, however, efforts by both the Pharmacist's Guild and Nazarick are underway to develop one.
 * Gazef Stronoff was infected by the gas, however, unlike most cases where monsters go feral, he was still able to retain his warrior instincts and utilize his Martial Arts.
 * The abnormal changes that subjects undergo once afflicted by the gas, is later revealed by Sophie Noia to not just be a poison but to also radically change the subject's race, being akin to a "curse". Attempts to resurrect subjects to restore them to their original selves have only shown that they remain in their contaminated states even after revival.
 * Later it was discovered by Sophie Noia, that the Melting Pot may have a process that could remove the contamination of the miasma and hence create a possible cure to the ailment. Currently the E-Rantel Magic Research Institute is researching on how to develop the cure. And later succeeded with Gazef Stronoff being the first cured patient.
 * Though more disturbing details on the cure were revealed later on during the region-wide miasma spread. It turns out that what cures a subject from the status of a Contaminated Beast is actually the souls of the dead. In those who have died tragically at the Chaos Beasts are required to release subjects from the affliction.
 * For the cure to work, the bodies of the deceased are needed which are combined with the Chaos Stones from Chaos Beasts, to trigger the decontamination process. The result only cures those strong enough to endure being contaminated and later gifts the cured with enhanced vitality and strength.
 * The cure requires the most freshest of corpses, as common knowledge in the New World, hold that the souls is released from the body and returns to the gods when it rots. Thus the current theory is that bodies which retain souls are an ingredient to the cure.
 * So far the exact contents of the cure has yet to be disclosed to members of the Tripartite Alliance as such revelations would bring about controversies, especially from the Slane Theocracy.
 * Those affected by the miasma and cured receive an immunity that allows one to be able to safely traverse through the "other side" of the Crack. However beings who were born from the Sea of Possibilities have been proven to be naturally immune to the toxicity.
 * Later it was shown that those, at least in Gazef's case, are given the side effect of breaking through to the threshold of the Realm of Heroes.
 * Additionally through some ploy of Enhela Read Gahi it has been shown that the miasma could be controlled, as later on entire cities in the Kingdom and Empire became engulfed in mists of the toxic gas.
 * The remnants of Zurrernorn in E-Rantel, dabbled in miasma researched and developed a "secret medicine" that could mutate ordinary sanitary slime to create a Super Giant Sanitary Slime, also known as Birth Slime, that was imbued with Negative Energy in order to restart the Death Spiral ritual.