"Hikaru in the Light!" centers on Hikaru Aoi, a high school student who discovers an ancient artifact that grants him the ability to manipulate light. This power, initially overwhelming and uncontrollable, becomes a focal point of his life as he learns to harness it. The artifact is tied to a long-forgotten prophecy involving a celestial war between beings of light and shadow, and Hikaru is revealed to be the chosen "Bearer of Light," destined to prevent the resurgence of a dark entity known as Umbra.

The narrative unfolds as Hikaru encounters other individuals connected to the prophecy, including Kaito Shirogane, a stoic and skilled warrior who serves as his mentor, and Yuna Hoshizora, a mysterious girl with her own ties to the artifact. Together, they form an uneasy alliance to uncover the truth behind the prophecy and prepare for the impending conflict. The story explores themes of responsibility, self-discovery, and the balance between light and darkness, as Hikaru grapples with the weight of his newfound role.

As the plot progresses, Hikaru faces numerous challenges, including battles against shadow creatures and rival factions seeking to exploit the artifact's power. The series delves into the histories of its characters, revealing their motivations and connections to the prophecy. Kaito's past as a former guardian of the artifact and Yuna's hidden lineage as a descendant of the celestial beings add layers of complexity to the narrative. The story builds toward a climactic confrontation with Umbra, testing Hikaru's resolve and the strength of his bonds with his allies. The series balances action, character development, and world-building, creating a cohesive and engaging narrative.