Umi Nakano attends acting school alongside Chizuru Ichinose. He maintains a generally calm and collected demeanor, only truly lighting up when discussing acting. His perceptive nature leads him to question Chizuru directly about her feelings for Kazuya Kinoshita.

Kazuya first encounters Umi during Umi's date with Chizuru. Later, learning of Kazuya and Chizuru's independent film crowdfunding campaign, Umi offers to retweet and promote it. His assistance comes with a condition: Chizuru must grant him a personal request, the specifics of which remain undisclosed.

Umi appears across multiple seasons of the anime adaptation and is also portrayed by Ryōsuke Sato in the live-action television drama. His surname "Nakano" translates to "middle field" or "wilderness," while his given name "Umi" means "sea" or "ocean." His documented interactions are confined to his connection with the acting school, his dealings with Chizuru, and his involvement in the film project.