The mentor and teacher who recognized Kai's talent when he was in elementary school and guided him toward becoming a pianist. He was once a brilliant pianist himself, but he lost his prime skills along with his fiancée in a car accident. The accident occurred when his fiancée, who was driving at the time, swerved sharply to avoid children running out from an alley, resulting in the car crashing into a guardrail.

A boy with a feminine appearance. He is friends with Shuhei Amamiya and comes from a poor family. He plays the piano for fun but possesses immense skill. He has his own unique style and is exceptionally talented. He loves the piano in the forest (which originally belonged to Ajino Sosuke). He loves and cherishes the piano. He is an elementary school student.

Originally lived in Tokyo but moved to the countryside because his grandmother's health declined. He met Kai there and became close friends. He is the only son of a wealthy family. His family includes his father, the world-renowned pianist Yoichiro Amamiya, and his mother, Namie Amamiya, a housewife who is presumed to be a former piano academy instructor and is very involved in his education. Unlike Kai, he plays the piano to achieve his dream of becoming a professional pianist. He loves Kai's piano playing. He is an elementary school student.

A character who felt anxiety and fear of losing when Shuhei appeared at a piano competition. She calls Kai by the name of her dog, Wendy. She likes Kai because she associates him with Wendy. When she feels nervous, she pets Kai's head. She is the daughter of a wealthy family. She plays the piano to gain recognition from her family. She is an elementary school student.

Kai's mother.