Miki is a young girl who lived in the slums of Shinjuku. Labeled as the "Lucky Little Ghost", those who meet her would fall for her smile, and are somehow befallen with good fortune later on. Previously, she lived in an underground section of Shinjuku Station alone after her mother had passed away several years before. After a hit-and-run accident, she would be adopted by Umibozu and would later on live with him at the Cat's Eye Cafe.
Miki is unaware of who her father was, though it was revealed later to the other characters that he was the King of an unnamed country. He often visited Japan while on business and fell in love with Miki's mother who worked in an old bar in a quiet area. Because the political situation in the kingdom was unstable, when she became pregnant, Miki's mother left her job and disappeared. She raised her daughter all alone in an abandoned underground arcade so no one would be able to find them if they discovered their existence. Miki's mother would later die in an accident and Saeko would be the first of our heroes to encounter the little girl. Much later after Miki starts living at the Cat's Eye Cafe, Ryo and Xiang-Ying would find out the King had been killed and replaced with a double. All these events are kept from Miki to protect her.
Although this Miki shares the same name as Miki in City Hunter, they are not the same character. Like the Miki in Angel Heart, the Miki in City Hunter was also an orphan and raised by Umibozu, though in City Hunter, this Miki is much older. Miki's hairstyle also appears to be similar to the original Miki in the third and fourth City Hunter series.

(Source: Wikipedia)