Kitamaru Kumi is a nine-year-old girl who has leukemia. She was awaiting an operation to get bone marrow from her older sister.

She was a patient in the same ward as Satoru. She watched Satoru go through physical therapy, encouraging him to try harder.
Nishizono Manabu wanted to kill her in a way to frame Satoru for murder once again; however, he underestimated his opponent and finally got caught.