Angelic Energy Disorder

From Kokorodatabase

Angelic Energy Disorder, or AED, is a genetic ailment that strikes, as the name implies, those with partial angelic DNA. Exertion of energy, especially the magical kind, is disproportionate to the action; in other words, too much energy is used even for simple tasks, therefore sapping the afflicted. Kitenshi Kocha has made it her mission to cure this, and Shirogane Ryou decided to help, mainly because the research could inspire a cure for Kyr's unwanted immortality. Both were eventually cured, although Kocha's AED cure is still in testing periods back in her world, and, as this is taking years, tension still exists as to whether she will be able to save her father; her mother, with typical disregard for authority, talked her into administering the cure anyway, and he is showing slight improvement.

Tenshi Kuro had this disease while he was in play, and in the dimension Kokoro Draft, where he still exists. Shirogane Misao also showed symptoms before she was retconned into a valkyrie and later dropped.