Hikaru Shidou is one of the three protagonists summoned to become a Magic Knight. She is an eighth-grade student living in Tokyo, where she helps her parents and her three older brothers, Masaru, Satoru, and Kakeru, run a family kendo dojo. Her training in kendo from a young age contributes to her proficiency with a sword. She has bright red eyes and scarlet hair, though her appearance in the original manga features pink hair instead. She is notably small for her age, which often leads to her being mistaken for being younger than she actually is. Her birthday is August 8.

In terms of personality, Hikaru is headstrong, determined, and possesses a passionate and enthusiastic nature. She is fiercely loyal to her friends and displays a remarkable amount of courage, often being the first to rush into a battle or accept a difficult challenge. Despite her bravery, she can be quite childish and innocent, sometimes missing social cues that her companions Umi and Fuu understand immediately. Nevertheless, she is also considered the most strong-willed and mature of the group when it comes to making difficult decisions about the fate of Cephiro. Her pure and honest heart is presented as her greatest strength. She also has an ability to understand the language of animals, forming a strong bond with the creature Mokona and other fauna of Cephiro.

Hikaru’s primary motivation in the first part of the story is to save the world of Cephiro so she can return home to her beloved dog, Hikari, whom she considers her best friend from her life in Tokyo. She is the most eager of the three girls to accept the duty of becoming a Magic Knight, showing no hesitation when the task is explained to her. Her role in the story is that of the leader and the emotional core of the Magic Knights, often encouraging Umi and Fuu with her optimism. As the Magic Knight of Fire, she is destined to awaken the Rune-God (or Mashin) named Rayearth, the lord of flames who resides in the Fire Temple.

Throughout her journey, she develops significant relationships with her fellow Knights, Umi Ryuuzaki and Fuu Hououji, becoming best friends with them. She also forms a close friendship with the creature Mokona. In the second half of the series, she meets Lantis, the younger brother of Zagato, and falls in love with him, a feeling that is much more overt in the anime adaptation than in the manga. She also develops a strong friendship with Eagle Vision, the leader of the invading nation of Autozam, and feels a deep sympathy for his cause.

Hikaru undergoes significant character development. After the traumatic climax of the first arc, where she is forced to kill Princess Emeraude, she is devastated by guilt and horror at her actions, leading to a period of depression and silence at the beginning of the second arc. This internal conflict becomes a central theme, culminating in the creation of Nova, a shadowy duplicate materialized from Hikaru’s own sorrow and guilt in the anime. Hikaru must learn to accept Nova as a part of herself rather than destroy her, eventually integrating the darker aspects of her heart back into her being. Her journey concludes when she is chosen to become the new Pillar of Cephiro, the sole individual whose will supports the entire world. Rather than accept this role, she uses her godlike power to abolish the Pillar System entirely, deciding that the fate of Cephiro should be supported by the combined will of all its people and not dependent on the sacrifice of a single person.

As the Magic Knight of Fire, Hikaru’s notable abilities include a variety of fire-based spells. Some of her primary attacks are Arrow of Fire (Honoo no Ya) and Crimson Lightning. Her primary weapon is a sword, which she wields with skill due to her kendo training. After a certain point, her sword is upgraded to one that will burst into flames if anyone other than herself touches it. She pilots the Rune-God Rayearth, a powerful mecha-like entity, in battle.