Kenji Tomosaka is the central male character of the story, a second-year high school student living in a quiet coastal town. His background is rooted in this setting, having moved to the town as a young child where the sea, shimmering under the summer sun, reminded him of ramune lemonade. It was there that he first met his neighbor and lifelong companion, Nanami Konoe.

In terms of personality, Kenji comes across as a somewhat carefree young man, but this exterior masks a deeper sense of responsibility and a natural inclination to look after those around him. He is notably shy and reserved when it comes to expressing his true emotions, particularly his romantic feelings for Nanami. To conceal this vulnerability, he often hides behind a facade, acting rude or obnoxious and teasing her instead of being sincere. His motivations are not driven by grand ambitions but by a desire to preserve the simple, precious rhythm of his daily life and his relationship with Nanami, which he values above all else.

Kenji's role in the story is defined by his long-standing, evolving relationship with Nanami, which serves as the core focus of the narrative. His days are spent in her company, whether walking to and from school or working alongside her in her family's vegetable field on the outskirts of town. He is a fixture at the Konoe family's local restaurant and also works as a mechanic, showcasing his practical skills. His life is intertwined with a few key figures in this small community. His closest relationship is with Nanami, his childhood friend and love interest. He is also the older brother of Suzuka Tomosaka, who helps keep the family together, and the cousin of Hikari Nakazato, a popular girl who often tries to push Kenji and Nanami closer together.

Throughout the story, Kenji experiences little in the way of dramatic, overt change. Instead, his development is subtle and lies in the gradual strengthening of his bond with Nanami as they navigate the unspoken tension in their friendship. Their shared memories accumulate over time, and the story explores the depth of their connection, highlighting the resilience of their relationship as they face the challenges of everyday life. Regarding notable abilities, Kenji is portrayed as mechanically inclined, owning a vintage Triumph motorcycle that was passed down to him by his father. He has desired this bike since childhood, though it is a notable trait that the machine is perpetually in need of repair, a fact that speaks to his persistence and mechanical hobby. No other significant or extraordinary abilities are detailed in the available information, and a detailed account of his character development is also not available.