Kagami is one of the main characters in Lucky Star and also the fraternal twin sister to Tsukasa Hiiragi.
Kagami Hiiragi has excellent grades in the school that she and the other main characters of Lucky Star attend. She is shown to study very hard in order to maintain these grades and she was even the class president in her first year. Despite her academic abilities she is still weak in housework and cooking and home economics is her least favorite subject. She has always been in a different class from her friends and, even though she denies it, it bothers her enough that she chose the humanities course in her second year so that she could be with them. Kagami was the only one separated into a different classroom; the same occurred in her third year. She often goes to their class during lunch to eat.
Kagami is the stereotypical "tsukkomi" character, however, she is prone to become shy at times, hence being a tsundere character as well. She enjoys video games, but plays a different genre than her friends, namely Konata: Kagami likes to play scrolling shooters. She also loves to read light novels. She sometimes feels lonely that no one around her shares her interests.