Riku Harada is the elder of the twin sisters. Unlike her younger sister Risa, who is more interested in fashion and relationships, Riku focuses on athletics, particularly lacrosse, and excels academically. She can be described as a bit of a tomboy, acting less girly compared to Risa. Riku is more serious, independent, and down-to-earth. Her hair is shorter, reaching about shoulder length, contrasting with her sister's longer locks. She also exhibits greater stamina and fitness, often biking to meet her sister at the train station and then jogging the rest of the way to school, while Risa prefers to be chauffeured and rides Riku’s bike for convenience.
Riku is known for her kindness, caring nature, and outspoken personality. She is selfless and always wants the best for everyone around her, eagerly helping those in need. However, she harbors a strong dislike for Dark Mousy. This stems from their first encounter when he saw her after she had taken a shower and unexpectedly stole her first kiss. In the anime, this happened when he landed on her balcony, startling her, and kissed her to avoid drawing attention. In the manga, the incident occurred when he hid in her room to escape the police, and she woke up during the encounter. The fact that Dark took her first kiss intensified her extreme dislike for him.
