Riko Akasaka is the sole daughter of the Akasaka style dojo owner. Originally enrolled elsewhere, she transferred to Nanyou High specifically to repay a debt to Takashi Mitsuhashi. Despite her small size and unthreatening appearance, she wields impressive aikido skills, easily handling most delinquents alone. Highly popular at her previous school, her constant association with Mitsuhashi at Nanyou led peers to view her as unconventional. Initially quiet and reserved, prolonged interaction with Mitsuhashi gradually transformed her into a brighter, more expressive person. She harbors romantic feelings for Mitsuhashi, consistently supporting him and using the unique affectionate nickname "San-chan" – derived from the alternative reading "san" for the character meaning "three" (三) present in his surname Mitsuhashi (三橋). Mitsuhashi frequently intrudes upon her home and dojo, initially irritating her father, though he eventually grew accustomed to his presence. Her bond with Mitsuhashi deepens throughout the series. During the Saipan arc, she becomes fiercely protective when he faces serious threats. On the Kyoto school trip, she actively pursues him to confess her feelings directly. By the final story arcs, their emotional connection becomes unmistakably mutual, culminating in them confronting the antagonist Sagara together as a united front. Ryō Tanaka, another student at the Akasaka dojo who holds unrequited feelings for her, transferred to Nanyou High alongside her. Despite Tanaka's strong sense of justice and dedication, her romantic focus remains exclusively on Mitsuhashi.