She is in the same class as Konata Izumi and excels in cooking.
Kagami often uses the term "birds of a feather" to describe the similarities between Tsukasa and Konata, mostly their bad habits.
She once received a mobile phone for her birthday, but didn't have much luck with it, as the phone was taken away by using it in class and later mistakenly ruined by putting it in the laundry, along with her skirt.
In spite of all this, she really does care about Konata, and is almost always willing to go places or do favors for her. 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.
She loves to read light novels, but is lonely, as no one around her has the same interests as her (though she is implied to have a knack for anime, since a stuffed Bonta-kun doll from Full Metal Panic! Kagami became the 2008 Anime Saimoe Tournament's champion with her sister Tsukasa being runner-up.
Additionally, Kagami chose the humanities stream in her second year, so that she could be with her friends, Konata loves to irritate her, and their arguments act as one of the main factors of comic relief throughout the series.
Kagami is usually annoyed by Konata's constant references to her otaku interests, but usually has an idea on what she is saying.
Her naivety, shyness, and kindness gets taken advantage of at times.