Masa Ikariya, nicknamed "Ikamasa," is the third-year captain of the Prefectural Umineko Commercial High School (Umisho) swimming team. He possesses a muscular physique, standing 182 cm tall and weighing 80 kg, with black hair and grey eyes. Ikamasa exhibits an intense obsession with shaving body hair, insisting it reduces water resistance for swimming; he practices this on himself and pressures teammates, causing frequent discomfort. His preference for extremely revealing Speedo-style swimwear and exhibitionist tendencies—often stripping during practice or competitions and urging others to follow suit—regularly provoke physical retaliation, especially from vice-captain Momoko Orizuka, cementing his reputation as the team's most disruptive member.

Despite his captaincy, Ikamasa's swimming ability is notably poor, consistently resulting in last-place finishes. His unserious approach prioritizes personal quirks over team development. Speculation suggests his leadership role originated from necessity; club founders Momoko Orizuka and Sanae Kise reportedly recruited him simply to meet minimum membership requirements, though Sanae's tendency to fabricate stories casts doubt on this account. Outside the pool, he shows an affinity for Mahjong. Emotionally sensitive, he often cries when confronted or disciplined for his antics. After graduation, the manga reveals he becomes a bar owner who assures Momoko his establishment will remain open whenever she needs to vent about her teaching career, indicating a sustained connection.