Hikaru is initially presented as being unpleasant, a brawler, and a tougher talker than Madoka. But once she becomes friends with Kyousuke, it is revealed that she's actually very kind and energetic. She accidentally sees Kyousuke perform an impressive physical feat using "The Power" and ends up falling for him quite hard.
She always refers to him by the English word "darling." She tends to revert to a form of baby talk, which is a signal she's extremely immature and shielded. She has an unrequited love for Kyousuke, and has been Madoka's best friend for several years since she and Yusaku Hino were the only ones who were never afraid of Madoka.
Her name refers to the brightness of the sun and of a sparkling personality. Hikaru is two years younger than Ayukawa and Kyousuke, and has the same birthday as Kyousuke.