Yu Ishigami is Shuchiin Academy's student council treasurer and an underclassman to the other members. The second son of a small toy manufacturer, he only attended school because his father forced him to, and was a truant until Miyuki recruited him to be treasurer. He usually keeps to himself and wears headphones while playing video games on his portable game console, however, he is a keen observer of people, noticing things that others do not wish to reveal, but occasionally getting in trouble for pointing out those things. He is afraid Kaguya might kill him because she tends to give him threatening glares and comments.