Hikaru Shido is a fourteen-year-old eighth-grade student from Tokyo and one of the three Magic Knights summoned to the magical land of Cephiro. She has bright red eyes and long scarlet hair, which she typically wears in a high ponytail. Hikaru is notably the shortest of the three heroines, a trait that often leads others to mistakenly believe she is younger than her actual age. She comes from a family that runs a kendo school, where she trains alongside her three older brothers, Masaru, Satoru, and Kakeru. Her bond with her pet dog, Hikari, is also very important to her.

Hikaru has an energetic, kind, and honest personality. She is headstrong and determined, often described as cheerful, brave, and possessing a very positive attitude. While she can be naive and childish in some ways, she also displays surprising wisdom and maturity for her age, which positions her as an unofficial leader among the Magic Knights. Her loyalty to her friends, Umi and Fuu, is fierce and unwavering. Hikaru is the most eager of the three to embrace her role as a Magic Knight and typically charges into battle with great enthusiasm. She is particularly fond of the creature Mokona, with whom she gets along best.

In the second season, Hikaru becomes deeply troubled by visions of Cephiro's destruction at the hands of a being named Debonair. This anxiety leads her to reunite with Umi and Fuu at Tokyo Tower, where they are once again transported back to the magical land. Upon her return, Hikaru meets Lantis, the brother of the late Zagato, who becomes a close ally and the focus of her romantic affection. The guilt and pain Hikaru carries from the events of the first season, particularly being forced to kill the previous Pillar, Emeraude, are so powerful that they manifest in the world of Cephiro as a physical shadow being named Nova. Nova is essentially Hikaru's dark side, embodying her repressed fears, insecurities, and suffering, and she is determined to claim Hikaru for herself, even if it means destroying everything Hikaru loves.

As the other Magic Knights deal with invaders from other worlds, Hikaru confronts Eagle Vision, the leader of Autozam. Despite being rivals, Hikaru shows her characteristic compassion by learning of Eagle's desperate need to save his dying world. She makes a pact with him, promising to help his people if she becomes the new Pillar of Cephiro. The central challenge of her journey in the second season is confronting and accepting Nova. Hikaru realizes she cannot simply destroy her shadow self without losing a part of her own soul. In the final battle, she approaches Nova not with a sword, but with understanding and love, embracing her darkness and re-integrating it into herself. This act of self-acceptance heals her spirit.

Ultimately, Hikaru is chosen as the new Pillar of Cephiro, a position that grants her godlike power over the land. However, believing that the fate of an entire world should not rest on the will and sacrifice of a single person, she uses her authority to abolish the Pillar system entirely, freeing Cephiro to be sustained by the strength of all its inhabitants. Before returning home to Tokyo, she confesses her love to Lantis and learns her feelings are reciprocated.

As the Magic Knight of Fire, Hikaru wields powerful flame-based magic. Her spells include the Arrow of Fire and Crimson Lightning. She is also a highly skilled sword fighter, having trained in kendo from a very young age. This physical prowess is enhanced by her remarkable jumping ability. Hikaru pilots the Rune God Rayearth, a colossal mecha that matches her fiery spirit in battle.