Koko used to be Sherry's closest friend. She was a very happy, kind hearted person who tried hard not to feel depressed with life. when Sherry tried to drown herself due to her mother's harsh words, Koko saved her. she encouraged Sherry to not throw her life away when times were harsh because there's always light at the end of the darkness. Since Koko was poor, she lived out in the streets trying to make a liveing. she even had to steal for money and food. despite Koko growing up in poverty while Shrry was rich, the two helped each other out in their lives. when Koko was finally accepted into a college, she met a mamodo named Zofis who told her that he could help her get back at all the people who abused her in life. Zofis then used his special powers to control Koko's heart and her think hurting others was fun. Koko was now a very cold-hearted girl, yet still seemed to be happy with her life due to her warped feelings. she proceeded to burn her own town and attempted to kill her friend Sherry. afterwards, she and Zofis left and began to formulated a plan that would make Zofis the mamodo king. Zatch and Kiyo learn this evil plan and have to stop Koko and Zofis before they destroy any more lives. elsewhere, Sherry proceeds to defeat more mamodo teams with Brago and is desperately searching for her old friend so she can free her heart from the darkness. She finally saved her. (Source: Zatch Bell! Wiki)