The story of "Onaka Hime" revolves around twin princesses, Berry and Flora, who lost their mother during childbirth. As they grow up, their father selects Berry to be the "Stomach Princess," possessing the ability to cure ailments and enhance the beauty of women across the kingdom with the aid of BifiX 1000. Disappointed at not being chosen, Flora continues to study in hopes of proving herself worthy. However, when Berry struggles to heal a sick woman using BifiX 1000, Flora seizes the opportunity to steal the product and try it for herself. Berry discovers Flora's intentions and reclaims the product before she can use it.