Motoko Aoyama (青山 素子, Aoyama Motoko?) is an intense 15-year old school girl, who practices the martial art of kendo, as well as being a member of the Shinmei-ryū sword school (which is also referred to in Akamatsu's later work Mahou Sensei Negima, as the school of the character Setsuna). Motoko is a resident at the Hinata Inn, living in room 302.
She has difficulty relating to other people, especially men, whom she finds to be a distraction that keeps her from being able to concentrate fully on her studies and practice. She also dislikes men because her sister left the dojo to marry. Her relationship with Keitaro initially resembles Naru's relationship with him in some ways; all too often he finds himself on the receiving end of various attacks as a result of his frequent mishaps or simply bad luck. She eventually warms to him somewhat and eventually finds herself developing strong feelings for him which she vehemently denies until near the end of the series. On two occasions this causes severe problems for both Motoko and Keitaro. In later volumes she develops a habit of writing trashy romance stories involving the two of them, often involuntarily.
Motoko has an older sister, Tsuruko, who gave up the life of the sword to marry. Tsuruko is far stronger at kendo than Motoko; Motoko both greatly admires and fears her older sister. However, Tsuruko believes that Motoko has more potential than she herself does, and that Motoko lost her drive to improve when Tsuruko married. Motoko is also the next in line to inherit the Aoyama family's Kyoto dojo as she is not married. It is notable that Tsuruko is actually Motoko's biological sister as they are two of the few characters in the series who are siblings by blood relation (the second siblings couple is presented by Kaolla and Amalla Su).
Motoko has only two serious fears in the world: Tsuruko and, for some unspecifed reason, turtles (even though Tsuruko correlates it to her intense dislike for men).
In the anime, Motoko is popular at her school for her kendo skills. She frequently spends time with Sachiyo Matsumoto (松本 幸代, Matsumoto Sachiyo?), Emi Ichikawa (市川 えみ, Ichikawa Emi?) and Kikuko Onoue (尾上 菊子, Onoue Kikuko?), who are all fans of her. Kikuko is especially protective of Motoko and has criticised Motoko's change in personality and decline in kendo skills since Keitaro began living at Hinata Inn, referring to him as a distraction. In the anime television series, Motoko is voiced by Yū Asakawa in Japanese and Mona Marshall in English.