The phrase refers to collections of printable outlines and illustrations depicting characters inspired by Japanese animation, with a focus on aquatic, mythological figures. These materials are designed to be colored in, typically by children or hobbyists, as a form of creative expression and recreation. These illustrations often feature stylized representations of mythical sea creatures with human-like qualities, drawn in a manner consistent with aesthetics popular in Japanese animation and manga.
The appeal of these illustrative outlines stems from the combination of two popular themes: the allure of underwater mythology and the distinctive visual style of Japanese animation. Engaging with these materials can foster creativity, improve fine motor skills, and provide a relaxing and enjoyable pastime. The concept also connects to a broader cultural interest in fantasy, mythology, and artistic expression through coloring.