Mors Vincit Omnia

Mors Vincit Omnia (Latin for 'Death Conquers All'), also known as MVO, is a condition in A Masochist's Tango marked by an excessive use of an ability to an unhealthy extent. Introduced in Episode 15 by Yawa Camellia, she explains that it can be spurred on by stressful and otherwise negative outside factors, but mainly occurs when "your ability [gets] the best of you". MVO causes the sufferer to become increasingly violent and unhinged, have their memories become 'muddled', and gain the addition of a certain number of rings around the retinas of the eyes depending on the severity of the situation. Anyone with an ability has a chance to contract and even die from the condition, but more mild cases can be easily treated.

Trivia

 * It is heavily implied that Asphodel Algea suffers from the condition, given her incredibly violent tendencies and the telltale rings in her eyes.