Sonoda first makes his appearance in Volume 6 of the manga when he accidentally bumps into Ayumu and immediately senses her distress. Shortly after, when Manami and her friends attempt to drag Ayumu into the bathroom, presumably to torment her further, Sonoda intervenes. With the support of several other students, he successfully defends Ayumu and confronts the girls. He then reveals that he has personal experience with bullying, which motivates him to stand up for Ayumu. However, he clarifies that his actions are not solely for her benefit; instead, he aims to alleviate his own pain through helping her.
Later on, Sonoda encounters Akira Karino, Manami's new boyfriend, and instinctively tries to flee from him. This reaction suggests that Akira was one of his primary bullies in the past. In Volume 8, Sonoda once again comes to the aid of Ayumu and Hatori but must confront his fears when Akira attempts to prevent the girls from escaping a burning building. After choking Sonoda, Akira turns his attention to the others, leading to a physical altercation between him and Sonoda. The fight ends with Akira hanging out of a window, and Sonoda expressing his deep hatred for him. Akira falls from the window but survives, while Sonoda rushes off to find Ayumu and Hatori.
Despite his traumatic past, Sonoda maintains a gentle demeanor, which is reflected in his passion for gardening. His favorite flower, the sunflower, holds significant emotional value for him. Sunflowers grow tall and free, reaching toward the sun, symbolizing the freedom and growth Sonoda aspires to achieve. As the story progresses, it becomes evident that Ayumu and Sonoda have developed romantic feelings for each other.
