As with all honne, Soku has three forms: a childlike form, an adult form, and an animal form.
Their animal form is a small dog with black and white fur. Their adult form is a willowy youth wearing a white shirt, a light green hoodie, sage-colored pants, black shoes, and green socks, with a tattered black tie around their neck. As a child, they wear white shoes and socks, chartreuse pants, and a gray hoodie, and their tie is neat rather than disheveled. In all three forms, they retain electric green eyes, dog ears, and a green, circular mark in their hair, covering their right eye.
Their appearance as an animal is based on Ai's dog Kuro, who looks identical save for having red eyes and lacking his honne counterpart's supernatural features.