What kind of illness was Kaori Miyazono suffering from? Does anyone know what kind of illness Kaori Miyazono was suffering from? According to the series' wiki, it is speculated that it was bone marrow failure,


   due to the change in her skin pigmentation and the need for an operation.
In my theory, her disease is Friedreich's Ataxia. Symptons begins between the ages of 5 to 15. Muscle weakness in the arms and legs and loss of coordination are symptons.

It causes heart disorders. In Episode 20, she may be having a severe and painful tachycardia, and a following cardiac arrest. The surgery may be to implant a pacemaker, but another arrest killed her during the surgery.