she dies of it.
As far as I can tell, it is not stated what it is. Did I miss it?
when she was very young she needed surgery
her surgery is related to her falling down in 7th grade.
she behaves in ways that are atypical for her. Sometimes female characters are played as mercurial, so this may or may not be a valid symptom.
she fell at the recital, after she played
she had paralysis in her legs, (likely accompanied peripheral neuropathy)
her parents knew it was terminal about a year before she died.
she regularly went to the hospital for treatment but has not (where I am in the series) lost her hair (suggesting no chemotherapy.)
the (alleged) color of the paths at the hospital (Totsuhara University hospital) are either green or white.
She could not control the twitching of her right hand, and that would make playing violin impossible.
Some others have suggested that the diagnosis is a variation on
ALS or prion disease.
Is there a reference that tells or at least gives strong support to say what the illness was?
It is likely this series is an
It may be that as a young child she had an astrocytoma (particular kind of brain cancer) for which the tumor was removed, and they thought it was complete, but either it returned or wasn't all caught. If so then it would have advanced, possibly into a secondary glioblastoma (stage 4 variation, very lethal, and has average time between diagnosis and end of quality of life of ~18 mo.)