Nodoka Saotome

Nodoka was very reluctant to let her husband take her young child away from her, on a training journey. The only way she agreed to let Genma take Ranma from her was to promise that he would train Ranma to be "a man among men." If Genma were to ever fail in this regard, both he and Ranma would commit seppuku (the Japanese ritual suicide by disembowelment). Nodoka agreed to this deal and would be the kaishakunin (beheading assistant) for her husband and son, hence the need to always carry the katana. She is then supposed to join them in death after their own lives are taken.