Character Voice: Yui Itsuki
She is introverted, bookish, and obsessed with anything occult. One night, Yoriko performed a ritual and summoned Mike, the self-proclaimed "Demon King". A contract was formed between the two of them, and now she is unable to part with her unusually-shaped companion. Against her will, Yoriko and Mike roam the city every night investigating the magical disturbance in the skies above Tokyo, causing mischief, and eating doughnuts.
While on break, Yoriko and Lilica decided to try summoning a low-level demon servant for Yoriko. She was a bit nervous to try such a ritual, but her fascination with the occult got the best of her. That night, the two of them got together, and Yoriko drew a magic circle on the ground. Before starting the ritual, however, she got nervous and ran to the bathroom. While Yoriko was busy splashing cold water on her face and talking to herself in the mirror for encouragement, Lilica was up to no good. She thought it would be funny to re-draw the incantation and not tell Yoriko. When Yoriko returned and began the ritual, she did not summon a low-level demon, but rather, she summoned Mike the "Demon King". Naturally, Lilica feels a little guilty about this.
During the game some characters refer to Mike as Michelangelo the demon king namely those of extensive background, connections to the dark arts, or vast knowledge about arcanas namely Kamui, Lieselotte, and Mildred. Most of the other characters call Mike and Kitty-Staff much to his annoyance.
Source: Wikipedia, "List of Arcana Heart characters," available under the CC-BY-SA License.