Like her older brother, she is very attractive and well-mannered, however she is actually a sadistic person. She dislikes boredom and is always acting in a half-joking manner. She is a 2nd Year at Seiran High School for Girls. She loves to torment the people she likes, such as her brother and Tobimaro Mizunokōji, with pranks and by creating bad situations for them. When she first appears, she had spent 2 days traveling by ox cart to deliver Shūtarō's forgotten (and now spoiled) bentō, and she will frequently go through such lengths simply to harass him. She also likes to take advantage of Ataru Moroboshi's flirtatious behavior, usually causing a riotous scene in the process.
She is almost always accompanied by her loyal Kuroko who carry out her every order with great skill, in stark contrast to Shūtarō's mostly incompetent Black Glasses Corps. They will set her bombs and traps for her and transport her, either with a kago or by two of them wearing a horse costume for her to ride. They do not only serve Ryōko though, as they are seen carrying out jobs in stories that only feature Shūtarō.
She will throw grenades and bombs at people while acting calm and composed, and yet will cry over them when they return to her charred to a crisp. She often acts in total secrecy without telling anyone of her plans, such as setting bombs in the giant Christmas Cake, turning the giant Christmas Tree into a firework, and retaliating to people by setting off bombs near them.
She also shows an interest in black magic, having used hypnosis and voodoo dolls to torment her brother. She also likes to collect rare and mysterious items. She possesses a sakura tree that she treats like a pet, feeding it sake and the legs of Shūtarō's pet octopi.
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- Ryōko makes a cameo in episode four of Creamy Mami as one of the top ten performers on television. She is number five on the list and her song is titled Loves Masquerade.