Yui Tada is one of the protagonist of the series and the little sister of Mitsuyoshi Tada.

She keeps her black hair in a bob. She has a bright and bubbly personality. Since losing both her parents, she has looked up to her grandfather and older brother as parental figures, and has a sibling-like relationship with the cat Nyanko Big. She enjoys mystery novels, and is currently into the "Sunflower Express Love Incidents" series.

She looks up to Yamashita and holds secret feelings for him. It seems she is trying to keep her crush a secret, but it is so obvious that everybody knows.