Polar Night：

Polar Night once believed she needed no one, but her obsession with technology brought her into contact with Polar Day. Polar Night wasn’t her real name—she adopted the alias because Polar Day was her partner’s given name. It was only through Polar Day’s death that Polar Night saw other flesh-and-blood people in the world, though this realization stemmed from extreme hatred. Initially, she intended to have String Light seek vengeance. But after losing her partner, she was forced into exposure among diverse people and relationships. During String Light’s modification, she realized everyone might be interconnected—each someone else’s “Polar Day.” Abandoning her revenge plan, she transformed String Light into a stage robot. She also found collaboration with Pulsar, an entertainment club at school, numbing herself through amusement. Later, she caught the school’s attention and began developing military technology. The stage duties were handed over to subsequent members, while she retreated to the deepest shadows behind the curtain, taking on roles in technical guidance and recruitment. She ultimately left campus after a summons and remains missing to this day.

Polar Day：

Before joining The School, Polar Day was the only child of a wealthy family. While spoiled, she was also expected to maintain a prim and proper image. After leaving home, her willful and rebellious nature remained, and no one ever again stifled her passion for weaponry. She and Polar Night hit it off immediately, exchanging weapons crafted by each other for combat, their fighting style exceptionally brutal. She wasn’t one to hide her abilities; she practically craved the entire school knowing just how powerful she was. She refused to offer technical support to anyone besides Polar Night, earning her a notorious reputation on campus and making many hate her. She was aware of the numerous enemies she had made, but she viewed it as part of her fame. During a campus war, she lost contact with Polar Night, became trapped in the school auditorium, had her weapons seized, and ultimately died by her own weapons.

Bella ：

Having previously been overly enthusiastic in helping others only to have her assistance taken for granted, which wounded her pride, she now strives to appear less approachable. Yet her nature still compels her to frequently express concern and secretly assist others. She and Belilo were entrusted by Polar Night to take charge of Backstage Machina. While not a prodigy, she approaches tasks with diligence and retains everything she learns. At Backstage Machina’s base, she handles routine mechanical maintenance and security. Once she confirms an intruder, she shows no mercy. Her combat skills are formidable, but she never flaunts them before friends or strangers—using them solely for defense.

Belilo ：

Suffers from severe appearance anxiety, only removing his mask in front of trusted individuals. While he prefers metalworking over technology, his mechanical skills are no less impressive, specializing in machinery fabrication. An introverted individual who rarely ventures out, spending most of his time in the backstage area of the Backstage Machina base. He has built a comprehensive surveillance system to observe the external environment, though at the time of the story, monitoring is limited to the base—the school auditorium. He assisted Polar Night during the String Light modifications and holds Polar Night in high regard. His mask is self-made, featuring an axolotl design inspired by its regenerative abilities. He interprets this regeneration as a “spirit of indomitable perseverance,” though others find this notion incomprehensible.

He was sensitive about people asking about his eyes. They were disabled due to an electrician’s mistake, and he hated them. But if you asked, he’d still explain.