Arthur Yu is drummer for the Clockwork Toys, Wynter's middle school rock band in the spring semester of 2013 (02 Out of Tune). He is the first member she recruits, having heard him practice drums at school. His favorite band is Linkin Park.
Arthur is in seventh grade, whereas the other members are in eighth grade (although both Wynter and Hunter should be in ninth). He appears as a "startled javelina" when Wynter first speaks to him, but warms to her when she compliments his drumming as "really loud and confident". He doesn't believe his parents will approve and doesn't tell them for a while that he's staying behind after school to rehearse. On his suggestion, Wynter recruits Ethan on bass and Hunter on lead guitar. Arthur is impressed by Hunter's shredding, although Hunter later suggests to Wynter that they replace him with Hunter's older brother.
Ethan's younger sister is in Arthur's homeroom and calls Arthur after the graduation concert "just to chat" and "see what happens".
Arthur appears in 02 Out of Tune.