Overheat

, also known as, is a condition experienced by Third Generations as a result of overusing their Ignition Ability.

Overview
The flames of ones Ignition Ability are fueled by the oxygen in their own body. Should an individual use up a considerable amount of oxygen, they cannot use their Ignition Abilities again until they've regathered the oxygen to do so. When one has overexerted their Ignition Ability, it can potentially lead to burning their own bodies and severe dehydration.

When a Third Generation overuses their ability, their body begins to char due to the lack of oxygen in the body. This is a type of disease called. The charring caused by Tephrosis appears to be permanent and in some cases, it prevents the Third Generation from using their ability without feeling a great amount of pain. Although, in certain cases, Tephrosis actually grants the victim new pyrokinetic abilities, such as generating smoke.

Konro Sagamiya
Lieutenant Konro Sagamiya of Special Fire Force Company 7 overheated during a battle with his Doppelgänger, a Demon Infernal. His upper torso was charred and he now cannot use his flames without causing himself great pain.

Kurono Yūichirō
Yūichirō Kurono of Haijima Industries overheated through unknown circumstances. His right arm was charred and rather than making it painful for him to use his flames, his Tephrosis actually granted him the ability to generate and control Black Smoke.