A schoolgirl turns into a cat to approach the boy she likes, but time spent in that form begins to threaten the boundary of her human life.
The magical disguise makes one kind of closeness possible while leaving her human feelings unspoken. Remaining a cat can no longer be treated as a consequence-free way to visit someone.
The transformation appears to solve a problem of approach: the girl can enter a relationship under a form that asks for less explanation. It also leaves the person she likes unaware of the full meaning of those visits. As the boundary between forms weakens, concealment changes from a convenient trick into a choice with costs. Consider it for a romantic fantasy connecting a literal change of body with the difficulty of being recognised as oneself.