Runa Kusami, nicknamed Tsukimi, attends Toshobu High School. She possesses short light blue hair featuring a single long braid on her right side, light blue eyes, and typically maintains an emotionless expression. Her stature is notably short.

Tsukimi exhibits a consistently stoic and quiet demeanor, frequently seen alongside her friend Cherry while participating in Cherry's activities. She communicates with simple, frank speech, delivering remarks directly without hesitation—even when her bluntness risks offending others.

Within the series, she appears selectively in background or supporting roles. She is observed during a date montage involving Joro and Himawari, dining at a family restaurant with Yasuo Hazuki (Hose). Later, when Joro loses Pansy's book at a shopping mall, Tsukimi and Cherry aid in the search. By evening, they recover the book; she informs Joro of its discovery in a damaged, "beaten up" state.