Hiyariko assists Doctor Hiyari, a mad scientist conducting unusual experiments from a castle, typically to aid Baikinman. Her sole documented appearance occurs in the 2008 movie short "Sore Ike! Anpanman: Hiya Hiya Hiyariko to Bafu Bafu Baikinman." During this event, she attempts to provide Baikinman with a specialized spray designed to greatly increase his size. The experiment backfires when she administers the spray incorrectly, resulting in Baikinman's transformation into an infant state. This incident constitutes her only significant recorded action.