Rio Ueda () is a third year (senior) who used to live in Tokyo and Kakeru Naruse's ex-girlfriend.
Rio has chin-length reddish-brown hair and light brown colored eyes. She is often seen wearing mascara and lip gloss.
To most of the school, Ueda is seen as a upbeat, friendly and playful girl. However, to Naho Takamiya and her friend group (Naho especially), Ueda is a cruel, relentless bully, whose only intent is making Naho's life miserable and to keep her from dating Kakeru Naruse, even after she and Kakeru had broken up. On multiple occasions, she is seen harassing Naho, such as when she purposely shoved Naho to the ground or tried stealing the hair clip Kakeru gave her. She is also shown to be very possessive and easily jealous, as seen when she argues with Kakeru for 'being friends with Naho while he's dating her.' She doesn't stop her behavior until Takako Chino threatens to expose her true personality to the whole school.
After Ueda confesses to an underclassman who was a year younger than her named Kakeru Naruse, she became his girlfriend and talked to Kakeru more frequently where she is often hugging his arm and inviting him to cafes. She became possessive over Kakeru very fast. Eventually, due to this behavior, Kakeru realizes he only accepted her confession due to her appearance and they break up. Later, in her fight with Takako Chino, she states that 'Kakeru was only ever good for his looks.' Whether this statement was true while they were dating or if it was simply her dying argument trying to defend her behavior is unknown.
She is suspicious of Naho Takamiya.
- The name Rio means "white jasmine" (莉) or "village" (里) (ri) and "center" (央), "thread" (緒) or "cherry blossom" (桜) (o).
- Rio's surname Ueda means "above, top, upper" (上) (ue) and "field, rice paddy" (田) (da).