Yuuko Yoshida, also known as Shadow Mistress Yuuko, is the protagonist of the anime series 'Machikado Mazoku'. She is a high school girl who one day awakens to her demonic powers, discovering she is a descendant of a dark clan. Despite her newfound powers, Yuuko is clumsy and not very powerful, leading to humorous situations. Her mission is to defeat a local magical girl, Momo Chiyoda, but they end up becoming friends. Yuuko's journey is about self-discovery and embracing her heritage while forming bonds with those around her.