Zenjirou Ikeda serves as an apprentice in Katsushika Hokusai's Edo-period art studio. This young artist cultivates a close relationship with Hokusai's daughter, O-Ei, through their collaboration on art projects. Zenjirou possesses a reserved and quiet demeanor, frequently expressing himself through small gestures like bringing food or assisting with artistic tasks rather than extensive dialogue.

His patient and supportive personality contrasts with O-Ei's independent, non-conforming nature. Zenjirou's kindness and understanding offer crucial emotional support to O-Ei, especially as she pursues her artistic ambitions within her father's shadow. While never explicitly declaring his feelings, his consistent actions demonstrate care and commitment to their relationship.

As an artist under Hokusai's mentorship, Zenjirou dedicates himself to his craft with a serious and practical approach, reflecting a strong sense of duty and adherence to traditional methods. He later gains recognition for his specialization in the bijin-ga genre, focusing on depictions of beautiful women.

Zenjirou's life concludes approximately one year before Hokusai's death, with historical records indicating he achieved a degree of fame for his artistic contributions during his lifetime. His role underscores themes of support and partnership, particularly in relation to O-Ei's struggles for recognition.