Since I haven't had the chance to read 'the sandcastle graphic novel', it's hard to say precisely. However, it could be a story of creativity and imagination. The sandcastle could be a focal point for a story that delves into the minds of the characters. For example, a young artist might be using the sandcastle as a form of self - expression. The graphic novel could then explore themes of art, self - discovery, and the transience of creations as the sandcastle will eventually be washed away by the sea.