Nagisa Natsunagi

As a child, Nagisa had a heart condition while she also had a weak and fragile body which forbid her from going outside and to school meaning she spent most of her childhood in a ward room's hospital bed. One year before meeting Kimihiko Kimizuka.

[Spoiler] Nagisa received a heart transplant from an unknown donor that later was revealed Siesta was the donor. She inherited one of Siesta's "Seven Tools", the musket gun. [/Spoiler]