Her family's freehold was next to that of the Zivonik family. Tragically, her parents and her two older brothers were killed in the last wave of the Manticoran Plague. After the deaths of her parents and siblings the Zivonik family adopted her, and she was in a close relationship with their son, Karl.
Just before a sledding outing with the younger Zivonik children, Sumiko and Karl had a big fight because Sumiko thought they should get engaged when she turned fifteen, while he wanted to wait until they were both legally adults. Later during the trip, Sumiko noticed a crown oak branch falling towards Larissa, one of Karl's younger sisters. She tossed the little girl out of the way, but was herself crushed by the branch, dying almost instantly. (SK1, SK3)