Yumi is a Fillmore! character, and an X Middle School student.
A year before, Yumi gets the idea of making a virus to reveal secrets of the Haves, or the Popular Kids, to show that "everyone is ugly".[1]
Her friend Gladys grows scared of the virus and what the project is doing to Yumi. Over the summer Gladys becomes Alexis Bixby, a popular kid at X School in hope that Yumi would not find her. When Yumi discovers her, she threatens to reveal Alexis' identity as a make-over computer nerd to her new friends unless Gladys helps finish the "Electric Haircut" project.
She goes into the school's computer system and removes every trace of Alexis. Fillmore talks some sense into her, and she stops her virus. When Jonah, Gladys, Yumi and Maryanne enter the Safety Patrol, she remarks that Principal Folsom is talking to her parents and "if she winds up with detention until high school", she would be lucky. She tells Fillmore that she said "sorry" to Gladys and then apologizes to him. She thanks Fillmore for "Making a good argument."