Yoko is a human with powers that could potentially cause cataclysmic destruction. He is a young adult who goes to a sort of superhero school (Kinda like MHA) Where he studies hard and doesn't have much interest in shenanigans.
Yoko's power is a demon, made entirely of emptiness and dark thoughts, trapped inside of his body. While Yoko does have control, Mephistopheles (The Demon), can influence his thoughts and actions under certain circumstances. His powers work like an extension of his body, allowing him to cast the shadows in and out at his own will. However, The Demon requires minor tribute for power. Yoko's emotions are nearly nonexistent, causing him to become sociopathic. Along with that, dark thoughts and negative emotions are drawn from passersby. These emotions and thoughts are in a sense, absorbed by the demon, but with so many dark thoughts floating around, Yoko
is living in a constant state of darkness. Yoko wants only one thing, to make people happy, because he can't be. He enjoys cooking, working out and other little things.