A third-year student at Trinity General Comprehensive Academy and the head of the Library Committee. An expert in deciphering and restoring ancient documents, she is known by the nickname "The Magician of the Old Library." In the story, she performs miracles by restoring items from a state where they barely retain their original shape to perfection in a short time. In one account, it was mentioned that she could even restore shattered antique tableware, though it remains unclear if that specifically referred to Ui or if it was a rumor that grew legs. She usually stays holed up in the Old Library, analyzing, restoring, and managing ancient books. Her attachment to old books is greater than anyone else's; she treats them not as "objects" but as "living beings" and cherishes them deeply. She is a textbook shut-in and introvert. She prefers dark, narrow spaces and is a homebody who dislikes bright or dazzling things. She often works through the night, and dark circles are visible under her eyes. She has a streak of misanthropy and is fundamentally suspicious and aggressive. She even looks down on the common masses of students to some extent. She is somewhat of a conspiracy theorist and holds prejudices, especially against the Sisterhood, which is never short of dark rumors. Because of this, she tends to cast a suspicious eye on everyone. Her weapon is the "Volume Suppressor." The model is the De Lisle carbine, a British-made suppressed rifle for special operations. She reportedly uses it to silence targets when the surrounding noise becomes too loud. It is a bolt-action pistol-caliber carbine that uses .45 ACP rounds.

A first-year student at Trinity General Comprehensive Academy and one of the librarians belonging to the Library Committee. One of the few students who has read every single book in Trinity's vast collection. She speaks passionately about books and occasionally lets a spoiler slip regarding parts the other person hasn't read yet, but fundamentally, she is a considerate person who cares about providing a high-quality reading experience. She gets quietly furious at those who treat books poorly. She loves recommending books to others as much as she loves reading them, to the point where her first thought upon meeting someone is "What book would suit this person?" As a librarian, she finds fulfillment and joy in finding and providing the optimal book for the knowledge or information others need, truly showing her worth when searching for books not listed in digital databases. Perhaps because she has read so many books, she has a high tolerance for works with extreme depictions. Her assault rifle, "Library Ruler," is based on the SCAR-H. Among Trinity students, Yoshimi also carries a gun with the same motif, but Shimiko's gun has a more customized design.