My Purple Mermaid is about a boy named Marshall (the reader), a bored kid stuck in the monotony of daily life. He spends his days helping his father run a fish shop, attending school, and hanging out with his best friend, Andy. Both boys are fascinated by the mysteries of the undersea world. Marshall's life takes a dramatic turn when he becomes the target of a bully named Lars, who one day pushes him into the ocean. To his shock, Marshall encounters a mermaid who rescues him and helps him return home. As their friendship blossoms, the mermaid introduces him to the wonders of her underwater world, giving him a sense of adventure and purpose he's never known. However, danger lurks on the horizon. Marshall and Andy must work together to protect their new friend, Tsume, from a relentless ocean hunter determined to capture her. How far will Marshall and Andy go to shield their mermaid friend from harm? And what secrets will they uncover beneath the waves?