Kokoro Amatsu is a character in the anime ReLIFE. She is the homeroom teacher of Class 3-3 and the advisor of the girls' volleyball club at Aoba High School. Born on March 10, she is one of the youngest teachers at the school, beginning the story at 25 years old, and she specializes in physical education. Outwardly, Kokoro has an energetic and boyish personality with a strong will. She is mature and caring, effectively managing her classroom while offering advice to her students. She does not hesitate to assert herself, even when interacting with senior colleagues. Beneath this confident exterior, however, lies a sensitive and vulnerable side. She is easily discouraged and prone to crying, a contrast that defines her character as she works to mature into her role as a teacher. Her primary motivation is to be a dependable educator who guides her students through their final year. In the story, she acts as a supportive adult figure for the protagonists, offering a stable presence and an adult perspective on the challenges of high school life. Her key relationships are with her students, particularly Arata Kaizaki and Chizuru Hishiro, and with her colleague Kōshi Usa. She is deeply passionate about volleyball, dedicating much of her energy to coaching the girls' club. Her defining traits are her empathetic nature, her hidden sensitivity, and her strong commitment to her students.