Daisuke Mizushima attends Sakura-en Public Elementary School as a classmate of Hikage Miyakawa, appearing in the series' fourth episode. He possesses khaki-colored hair, green eyes, and typically sports a bandage on his nose. His mischievous personality manifests through teasing Hikage about her family's financial hardships. Despite this antagonistic behavior, a tsundere nature suggests underlying kindness beneath the surface.

Childhood friend Yukina Utsumi uses the affectionate nickname "Dai-chan" for him. Yukina holds an unrequited romantic interest in Daisuke, though he remains oblivious to her feelings. His teasing often involves exaggerated jokes about poverty, like suggesting Hikage would eat expired barbecue sauce. These jabs are consistently undercut when Hikage reveals her actual circumstances are worse than his mock scenarios, such as being unable to afford barbecue sauce entirely.

Daisuke has a younger sister and adopts a stray cat in the ninth episode, revealing a responsible aspect. His narrative role centers on comedic interactions highlighting Hikage's hardships. He maintains consistent light antagonism intertwined with subtle concern throughout the series, with no significant character development or relationship changes.