A Star Brighter Than the Sun is a Japanese anime television series based on the manga of the same name by Kazune Kawahara. The story centers on Sae Iwata, a girl who is physically stronger and taller than many of her peers, and her childhood friend Kouki Kamishiro. In elementary school, Kouki was a delicate and fragile boy who often relied on Sae for protection. Sae developed feelings for him, drawn to his gentle smile. However, as they progressed through school, Kouki experienced a significant growth spurt and transformed into a tall, popular, and charismatic young man. Feeling that he had become a distant figure shining out of her reach, Sae resigned herself to letting their close friendship fade.

The narrative begins in earnest near the end of middle school when Sae and Kouki are assigned to work together on a committee for the sports festival. This reconnection stirs Sae's long-dormant feelings once again. The situation becomes more complicated when they enter high school and find themselves in the same class. The story follows Sae as she navigates her deepening emotions while trying to suppress them, believing that Kouki is now too popular and out of her league. She struggles with her self-image, seeing herself as not cute or dainty like other girls, while Kouki continues to treat her with the same kindness he always has.

The main characters are Sae Iwata, whose gentle and caring nature is often masked by her tough exterior and physical strength. Kouki Kamishiro is a cheerful and genuinely nice boy who has grown into a confident and popular student, though he retains the sweet personality Sae admired as a child. The supporting cast includes their new high school classmates. Hisui Onodera and Mio Kagawa become close friends to Sae, offering her support and advice. Yota Ayukawa is another classmate, and the story also introduces Subaru Kamishiro, Kouki's cousin, who becomes a source of tension and misunderstanding.

The setting is a Japanese high school, where much of the series takes place. The narrative follows the characters through a series of typical school events that serve as milestones for their relationship. These include a class trip, a jump rope tournament, a cultural festival, and a class play. A notable narrative arc involves Sae learning that Kouki has a crush on someone he describes as a star brighter than the sun. Believing this person could not possibly be her, Sae resolves to support him from afar, leading to a series of misunderstandings as she tries to hide her own feelings. The first season concludes during the school festival, where a series of incidents and a confession bring Sae and Kouki to a moment of truth. The season ends with the two finally acknowledging their mutual feelings for each other.