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 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.

Trivia

 * However, there are no cases where the people of the Great Tomb of Nazarick becoming violent, including the protagonist who has no combat ability.
 * 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 to be a poison but also radically changes the subject's race or is 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.