Haruna's best friend since middle school, she is remarkably composed and serene, able to understand Haruna effortlessly. Their bond is exceptionally close, with Haruna recalling how Mami initially befriended her by assisting with her pitching skills. Working part-time at a video rental store, Mami was also the softball team captain. Haruna holds Mami in very high regard, considering her 'amazing.' She describes Mami as kind, intelligent, and tranquil, often leading others to label Mami as a 'nice girl' or a 'good girl.' It has been revealed that Mami cherishes her friendship with Haruna immensely, even expressing feelings of betrayal towards herself for doubting Haruna's pitch during their third year, which cost them a game.
Mami has repeatedly demonstrated her keen perceptiveness, particularly regarding Haruna. In return, Haruna shows her affection for Mami by trying to help her find love, resulting in a date with Asaoka due to their shared traits. The nature of Mami's relationship with Asaoka and their friendship remains unclear, but they seem to share a mutual understanding.
