Yui Rio is a NPC in Yandere Simulator. She is one of students Akademi High School.
Yui has red hair and eyes of the same color but with a lighter shade. Her hair is worn in a ponytail to her right. In game files, her bust size is 0.5, and it is the smallest in the game. YandereDev says that in real life Yui would have the bust size AA, which is also the smallest bust size. On her right wrist, Yui has a red friendship bracelet. She also wears red panties, red stockings and default uniform.
Yui has "Evil" personality. Being the only one in the game has this personality and it means that if she witnesses alone the murder, she praises Yandere-chan and assures her that she will not tell anyone what she saw and then escapes from school. The next day, she will be pleased with Yandere-chan, but she will not want to talk to her in order not to be involved in murder. If she sees the corpses, she will not even scare, she will just run and call the police. if she witnesses the murder, along with several other NPC, she may be one of four students who will stop the main character (probably only to not show his true nature to others).