Sia Moon (alternatively spelled Shea Moon) serves as the snake familiar to the Beast Knight Yayoi Hakudou. As a familiar, Sia Moon provides supportive companionship and advice to Yayoi. Her role specifically involves encouraging Yayoi to pursue her interests in anime, manga, and cosplay, and to express her feelings more openly. Sia Moon consistently displays a nurturing and positive attitude towards Yayoi, focusing on both her hobbies and her emotional development.