With her mother Akiko, Chinatsu was spending their days modestly but laughing together. She is now very busy with her daily life after enrolling in an art university. She is anxious about a creative novel assignment titled "memories of first love" from the university. For Chinatsu, her first love is her childhood friend, Kohki, however, she has a bitter memory of the words which Kohki said to her when they were in middle school. It became a painful lump that still sticks in her heart. Chinatsu desperately tries to channel this "lump" by expressing such feelings in her assignment. One day, her mother discovers a notice in Chinatsu's room that Chinatsu is to be "re-tested" for breast cancer. Her mother got more nervous than Chinatsu. A slight change in their daily routine takes place. Chinatsu feels the lump in her chest became a small heart beat with heat. But the small heart beat in her chest is getting faster.