Kagami's physique is average. However, she is usually concerned about her weight, counting every kilogram she gains or loses. Kagami likes to eat sweet food and she is often seen eating sweet food at night, such as chocolate Pocky sticks. Despite her concern about her weight, she has no willpower controlling her eating habit, resulting in an "eat now, fret later" attitude. She has long, purple hair with a ribbon tied into pigtails, though she used to have an ahoge at the beginning of the series, and unlike Konata, has sharp eyes. Kagami is the stereotypical "tsukkomi" (the straight and intolerant type) character, however, she is prone to become shy and lonely at times, hence possessing the tsundere (the tough but shy type) characteristic, as well.
Similarly to Konata, Kagami likes video games, but plays a different genre than Konata: scrolling shooters. She loves to read light novels, but is lonely, as no one around her has the same interests as her. Both Kagami and Tsukasa are left-handed. Kagami shares the name of her creator, Kagami Yoshimizu, and according to the creator, Kagami was his pen name in his school days, and had her personality thought out long ago.