Oiso is a diver from Matsue Village who was renowned for being the best diver in the village; that is, until she got breasts, which altered and slowed down her diving.
Oiso's skin color is darker than the rest of the cast's, which most likely comes from her being in the sun for a long time. She wears a white headband, a white open shirt tied at the bottom, and a red skirt.
Oiso is a laidback person who likes doing what she does best. She doesn't like her big breasts, mainly because they hinder her diving skills, but also because they don't give her the status that they grant to noblewomen in higher class circles. Once her breasts were removed, she was very grateful.
- She is voiced by Yuuko Kaida, who is known for playing Elizabeth Mably in the Freezing anime. Born in January of 1980, she was likely around 31 when voicing Oiso.
- It is implied that Oiso is under the influence of Chifusa's ChiChi Nagare/Togi enhanced breasts, this is likely considering Oiso's random sexual advances towards Chifusa always involved her fondling Chifusa's breasts.