Hikaru Tezuka serves as a member of the elite Library Task Force within the Kantō Library Base's Library Defense Force. He joins the Task Force alongside Iku Kasahara, demonstrating greater initial capability and composure during their early assignments.

Professionally focused on intelligence gathering and strategic operations against the Media Betterment Committee, he collaborates closely with fellow intelligence specialist Asako Shibasaki. Their professional partnership deepens into a romantic relationship, culminating in significant moments like a notable kiss.

A central element of his background is his estranged brother, Satoshi Tezuka, who leads the Library Futures Project. This organization advocates combating censorship through information management and political negotiation, contrasting sharply with the Library Defense Force's paramilitary tactics, creating a significant rift between them.

During the protection of author Kurato Touma, Hikaru engages in strategic countermeasures against censorship expansion. He operates alongside Shibasaki in complex maneuvers challenging the Media Betterment Committee's constitutional overreach; their coordinated, calculated tactics earn them the "Chessmaster" trope designation.

He maintains a consistently professional and reserved demeanor. Colleagues typically address him formally by his last name, while only family members use his given name, reflecting the series' cultural workplace norms. His unresolved conflict with his brother symbolizes the broader narrative struggle between militant defense of intellectual freedom and diplomatic reform.