Akiko (Tokiwa Takako) is a single mother living with her teenage daughter Chinatsu (Yoshida Mizuki). An aspiring novelist admitted to the university of her dreams, Chinatsu has been tasked with writing a piece on the topic of “memories of first love.” For Chinatsu, the memories of her first love with childhood friend Kohki (Okudaira Daiken) are bittersweet, tainted by what he said to her in middle school; however, a reunion with Kohki begins to bring the two closer again, leaving Chinatsu with a feeling in her chest that she decides to focus on in her writing.

Meanwhile, Akiko finds a notice in Chinatsu’s room stating that Chinatsu is to be retested for breast cancer, and her concerns grow.

Adapted from Yokoyama Takuya’s stage play of the same title, The Lump in My Heart explores the sensitive emotions of an adolescent, depicting the bonds of a mother-daughter relationship in the face of adversity while also engaging with the unusual but important topic of early-onset cancer.