An underclassman of Nee-san, Okappa is one of the members of the Model Club. She is a classmate of Makimaki and sits next to her in class. She is generally levelheaded and calm but is prone to getting really violent and monstrous when it comes to Nee-san's antics. Still, she is shown to have a gentle and caring side when Makimaki was experiencing a heartbreak.
She is weak against insects, especially large cockroaches. A model of a train rides on her head.