Koko was once Sherry's closest friend, a cheerful and kind-hearted person who fought hard against feelings of depression. When Sherry attempted to drown herself following harsh words from her mother, Koko rescued her. She encouraged Sherry not to give up on life during tough times, reminding her that there is always light at the end of darkness.
Living in poverty, Koko struggled on the streets to make ends meet, even resorting to stealing for money and food. Despite their vastly different backgrounds—with Sherry being wealthy and Koko growing up poor—the two supported each other throughout their lives. When Koko finally gained acceptance into college, she met a mamodo named Zofis, who promised to help her exact revenge on those who had mistreated her. Using his special powers, Zofis manipulated Koko's heart, making her believe that hurting others was enjoyable.
Now cold-hearted but seemingly content with her warped emotions, Koko set fire to her own town and tried to kill her old friend Sherry. Afterward, she and Zofis left to devise a plan that would crown Zofis as the mamodo king. Zatch and Kiyo learned of this evil scheme and sought to stop Koko and Zofis before they could cause more harm. Meanwhile, Sherry, with Brago by her side, continued to defeat other mamodo teams while desperately searching for her old friend. Her goal was to free Koko's heart from the darkness. In the end, Sherry succeeded in saving her.
