A first-year high school girl who gives student council president Kinako Urushima a dog whistle to be used in emergencies. Owing to her excellent hearing, Yoriko is the only one capable of hearing the whistle, even at great distances. She regularly takes care of Kinako and worries about her wellbeing. She is affectionately nicknamed 'Mayo' by Kinako (a portmanteau of her surname and given name). She has a pet hamster and is a member of a sports club.