Hikaru Tezuka is a member of the Library Task Force and is initially ranked Librarian First Class, but is later promoted to Chief Librarian. He is drafted into the Library Task Force at the same time as Kasahara, though shows himself to be much more capable in terms of knowledge gained in lectures, clerical work in the base's library, and in typical combat. He finds it hard to give credit to Kasahara in the beginning since she is not up to what he considers to be the standards of a Library Task Force member, though he later recognizes her improvement and be one of her best friends.

He has an older brother named Satoshi Tezuka, who is a part of the government's Library Future Planning Committee. He used to admire his brother, until Satoshi decided to leave home. Even so, Hikaru couldn't actually forget everything about him, as shown with him keeping the watch his brother gave him some time ago. Later on, with help from Shibasaki, he threw away the watch (actually, Shibasaki sold it) and thus decided to stop thinking about him.

Thanks to his brother's scheme, Hikaru got closer to Shibasaki while trying to make plans. In the end, he developed feelings for her (which is mutual), and even told his brother to stay away from Shibasaki.