Bitter Honey.

Akako, a shape-shifting goldfish in the form of a coquettish nymphet clad in diaphanous red dresses, naively plays the role of erotic muse and adoring pet for an aging writer seeking greatness. Things quickly get complicated for the odd couple, however, when the writer's deceased former student/lover enters the picture as a ghost and helps Akako realize her own desires, activating her agency and frustrating the one-sided male fantasy the writer is so keen to continue.