Ken is Yuuri's younger brother and the son of Takuro and Remi, proprietors of a Sunny Bell port town flower shop. Around five years old, Ken and Yuuri receive the Mary Bell Picture Book from neighbor Rose, a story about a magical girl aiding lost children. Worried about their parents' struggling business, the siblings wish together for Mary Bell's help, summoning her to their world. Ken then joins thrilling adventures alongside Mary Bell, Yuuri, and Rose's dog Ribbon, journeying between Sunny Bell and the Flower Magic World. He engages in community events and faces challenges like mastering bicycle riding and helping to save a dying tree. Moments highlighting Ken's family connections occasionally surface, particularly noting his resemblance to his father. During the series climax, Ken aids the effort confronting the Holy Tree of the Flower Magic World as it threatens Earth's plants, contributing to the collective action that persuades the Holy Tree to relent and supporting Mary Bell's choice to stay on Earth. Ken also features in educational OVAs centered on traffic safety and earthquake preparedness.