Ren Aikawa is a second-year student at Yaegasumi High School, one of the three main characters alongside close friends Yua Nakabeni and Homi Moegi. She stands 162 cm tall with short brown hair and brown eyes, usually wearing her school uniform and 60 denier tights. Her surname combines "indigo" (藍) and "river, stream" (川).

Personality-wise, Ren presents a cool demeanor but is fundamentally shy, struggling to refuse requests. This often leads her reserved nature to give way to compliance, resulting in reluctant participation or peer pressure situations.

She holds a part-time job, initially noted at a bar where her presence boosted clientele. Later information clarifies she works as a family restaurant waitress, where the busy environment sometimes prompts complaints about the workload. Her daily life navigates school, work, and friendships, with interactions highlighting reactions to teasing or unexpected events.

Notable scenarios across episodes include changing torn tights after a mishap, massaging her legs post-work, receiving an overwhelming foot massage from Yua, and attempting to reciprocate a Valentine's gift by wrapping herself in ribbon—only to become entangled. These depict her as reactive within the group dynamic, balancing part-time responsibilities with school life and friendships.