Isaki Magari

Birthday: December 23

Isaki Magari is a cheerful and active girl who is a member of the school's swimming and astronomy club.

[Spoiler] Isaki suffers from congenital heart disease (monoventricular disease) and was constantly hospitalized during her early childhood years. Even though her condition was stabilized after several surgeries, regular and frequent checkups are required. This, combined with an unknown life expectancy, is the cause of her insomnia. [/Spoiler]

(Source: Wikipedia, translated)