Reo Wakasa, nicknamed Reo-chan, serves as an engineering crew member aboard the destroyer Harekaze. She has shoulder-length blonde hair, purple eyes, and typically wears a headband featuring a four-leaf clover ornament on the right side, paired with a pink cardigan over her Yokosuka Girls' Marine High School uniform. Personality-wise, she exhibits a grumbling, talkative disposition, frequently complaining when situations deviate from her expectations. She maintains a straightforward, honest approach to her likes and dislikes and readily engages in gossip. Reo forms one-fourth of a close-knit engineering department quartet alongside Sakura Ise, Runa Suruga, and Sora Hirota. They regularly spend free time playing card games or mahjong, where Reo often employs frequent "chi" and "pon" moves, resulting in lower-scoring hands. Her fondness for the game is reflected in her favorite phrase, "north, south, east, and west." Her childhood in Miura District, Kanagawa Prefecture, was deeply connected to the sea; her father participated in yacht races, leading her to frequently ride small dinghies. After her parents denied her request for a small boat skipper's license during middle school, she enrolled at Yokosuka Girls' Marine High School to obtain maritime qualifications while pursuing her affinity for the ocean. Despite teachers recommending the navigation department due to her exceptional long-distance vision, she deliberately chose the engineering department. She holds a junior third-class marine engineer license and a junior second-class boiler engineer license, working specifically as a stoker. Academically, physics is her strongest subject, while Japanese is her least favorite. Her food preferences include seafood okonomiyaki, particularly with shrimp and squid, and sweet potato jelly, though she dislikes natto. She considers adding cheese or bacon to okonomiyaki "cheating" but will consume it if available. Her favorite color is cyan. Beyond her core friend group, she forms a significant bond with Rin Shiretoko in the light novels, eventually progressing to a first-name basis after shared experiences. The anime includes comedic moments featuring her in swimwear or underwear and a bath sequence where she reacts with surprise to a crewmate's physique. Her technical contributions focus on engine room operations, where she demonstrates consistent dedication despite her complaints. This role choice aligns with her rejection of navigation duties, emphasizing her preference for hands-on engineering work.