After 15 years, she returns to London only to find out that Ewan is dead and Arago has become a detective, trying to follow his brother's steps. Frustrated at first, she keeps a distant to Arago as she is not in favor of his decision of becoming a detective, and also feeling despondent because she was in love with Ewan.
However, after the ghost bus incident, Rio's behavior towards him changes and she becomes more friendly. She is one of Arago's closest companions, despite being kept out of the supernatural world. However, recently, Arago told everything that he knows; from his Brionac ability to Ewan's resurrection.
Rio is a young woman with short brown hair and yellow eyes. She is constantly seen with her hair tied into a ponytail and locks of hair falling on beside her face. Joe Sullivan states that she has a great figure.
Rio is usually seen to be worrying about Arago whenever he seems bothered. Being close to him since childhood, she notes that Arago has the tendency to scratch his ear whenever he lies, and feels downcasted whenever he hides something from her. She seems to have risen out of her depression, accepting Ewan's death, and joined the police force out of her own determination.
She treats Joe kindly, seemingly putting up with his perverted tendencies, and she's always there to support Arago whenever he needs it. She and Coco have grown close since they met, but she still throws a jealousy fit whenever Coco gets too close to Arago.
She was borned to a japanese mother and a english father, and moved to Japan 15 years prior to the series due to her father's work. She was called "Crybaby" Rio often as a child (mainly by Arago) because she tends to cry a lot. Even as a child she was in love with Ewan and dreamed of being his wife.
Being a half-japanese, she is the subject of teasing during her childhood (with the exception of Ewan). Arago, especially, often teased her as a child and bullied her by doing many things such as placing a bug on her, eating her apples despite knowing she loved them, and always flipping up her skirt. Despite this, Arago actually saved her from being bullied by other kids when they lock her up in a storage.
She is deeply in love with Ewan. Upset of his death, Rio keeps on lashing out on Arago; to the point where she despised Arago for living instead of Ewan. She still hold her feelings for Ewan and keep on saying that he is the most important person in her life. She even goes as far as to avenge Ewan's death and nearly becomes obsessed with investigating the case and anything about Patchman; which causes conflict with Arago.
She can be quite insensitive, often saying things to hurt Arago even when she doesn't realize it; although when she does, she apologizes for it. She is known to be stubborn and try to best Arago whenever they argue.
She also has shown to have feelings for Arago despite still loving Ewan. She always smiles and blushes around him especially when they get very close and shows acts of jealousy when Arago is with Coco. She also gets embarassed when it comes to Arago but does not understand why, hinting that she may not be fully aware of her own feelings for him.
She became a police officer and is apart of a special divison that specializes in using weapons as well as criminals who uses them.
For most of the manga, she specalizes in the use of firearms and was frequently seen usually using a handgun.
In the final arc, she used the werewolf pelt during the attack of the Couldren. In the last chapter of the series, it is known that Lepricaun adjusted the pelt so she can control it better and sucsessfully use it in battle.
Being one of her friend during her childhood, both Rio and Arago are very close to each other. When they were kids, she was often teased and bullied by Arago and was nicknamed 'Crybaby Rio' by him. Despite this, she was saved and eventually saved him on a few occasions. She is considered to be close enough to Arago to notice that he always scratches his ear whenever he lies. She always shows concern towards him and comes to realize that his many obvious lies is just his way to protect her. As the series progresses, her feeling towards Arago continue to grow, but try her best to deny it.
She and Coco are very close as they are often seen together. Although she seems jealous whenever Coco and Arago are together.
She is in love with Ewan and dreamed of becoming his bride. It is unknown if this feelings were mutual.
She and Joe have a good relationship. During a stake-out, she mentioned that she could already put up with Joe's perverted nature. However, this may be just be an excuse to accuse Arago to be the only one who is sexually harassing her as she is still shown to get embarrased whenever Joe spank her.