Ryunosuke Hanakuma serves as the vice-president of Tensho Academy's Swimming Club in his third year, despite being unable to swim and functioning primarily as the club manager. He possesses short, light brown hair featuring longer strands framing his face that reach his chin, violet eyes, and wears oval-shaped glasses. His standard attire consists of a dark blue jacket, light blue tie, white undershirt, patterned pants, and brown laceless shoes.

Intellectual and observant, Ryunosuke is frequently seen reading books by the poolside while carrying a handbook. He provides common sense and structure as a grounding influence for club members. However, he displays a snarky sense of humor, particularly targeting club president Takato Kiyosu, whom he often teases about his fear of ghost stories. Ryunosuke actively encourages others to share ghost stories to unsettle Takato.

He considers Takato Kiyosu his best friend and closest relationship. Acting as the calmer counterpart, Ryunosuke manages Takato's impulsive tendencies while still participating in his antics, including joint attempts to flirt with girls. Ryunosuke admits this activity amuses him because it tests whether Takato can succeed despite the disadvantage of Ryunosuke's presence. He also shares Takato's concern about improving the Swimming Club's point standings.

He appears briefly in Episode 5 alongside other Swimming Club members during a sequence involving the online game Cat Walk, where he remarks on Itto Takatenjin's academic abilities, noting Itto's higher grades compared to his own performance as a sophomore.

His interests include reading, and his favorite food is Torisoboro-don (a Japanese chicken rice bowl). The etymology of his given name Ryunosuke incorporates "dragon" (竜), "this" (之), and "forerunner/herald" (介), while his surname Hanakuma combines "flower" (花) and "corner/nook" (隈).