Ken is one of the two young siblings who serve as the primary human protagonists in the series. He is a young boy, approximately five years old, and is the younger brother of Yuuri. His physical appearance is that of a typical young child, with brown or black hair and black eyes. He lives in the coastal port town of Sunny Bell with his family.

Ken is a member of a family that has recently moved to town and opened a flower shop. His father is named Takurou, and his mother is named Remi. The family flower shop, which is also struggling financially, is named after the fairy tale character Mary Bell, a story that Ken and his sister love dearly. The family's neighbor is an elderly woman named Rose, who owns the Mary Bell picture book that plays a key role in the story's beginning.

In terms of personality, Ken represents the eager and sometimes mischievous energy of a young boy. As the younger sibling, he often follows his sister Yuuri's lead but is a willing participant in the adventures that unfold after the arrival of the flower witch. He is present from the very beginning, joining his sister in wishing for Mary Bell to appear and help their parents' struggling flower shop, a wish that is unexpectedly granted. This event sets the entire narrative in motion, positioning Ken as a fundamental character who helps bridge the human world with the magical world of Mary Bell.

Throughout the series, Ken is a constant companion to Mary Bell and his sister, participating in the various adventures that take place in both Sunny Bell and the Flower Magic World. His role is that of a human friend and supporter of Mary Bell. He is not a passive character, however, and he sometimes receives direct assistance from Mary Bell. In one instance, Mary Bell uses her magic to help Ken learn how to ride a bicycle. This demonstrates his role as a young child still learning and growing, with Mary Bell using her powers to help him overcome everyday childhood challenges.

Ken's importance extends into the climactic finale of the series. When the Holy Tree from the Flower Magic World attempts to remove all plants from Earth, Mary Bell is apparently killed. In a crucial turn of events, Ken and Yuuri travel to the Flower Magic World and are instrumental in her resurrection. This act underscores his deep bond with Mary Bell and his crucial role in saving the day. In the end, after the Holy Tree is calmed and peace is restored, Ken, along with Yuuri, Tambourine, and Mary Bell, are seen together happily reciting Mary Bell's famous catchphrase, signifying their enduring friendship.