Tezuka Guo Yu is the younger son of Ayana and the protagonist of the story. At eight years old, he is the youngest in the Tezuka family. He is described as having a handsome face and an earnest demeanor that mimics his brother's seriousness. Guo Yu had been homeschooled but expresses a desire to attend school after watching cartoons where characters go to school. He is cheerful, obedient, and easily pleased, as shown when he accepts candy from Coach Ryuzaki and greets the tennis club members. He has a close relationship with his brother Kunimitsu, holding his hand and seeking praise. He also has a childhood friend, Echizen Ryoma, with whom he reunites at school. Guo Yu is the top scorer in the entrance exam and is considered a mysterious figure by the tennis club members.
