Seventeen-year-old civilian Prof. Testa Lielbelle possesses exceptional intelligence, specializing in linguistics and cryptanalysis. His mastery of every language spoken by World War II participant nations secured him a university professorship despite his youth, though his boarding school years were marred by bullying due to his intellect.

Recruited into the Allied Cryptanalysis Department by Sergeant Alex Rossa, Testa tackles the Luger Code—an impenetrable communication system used by humanity's enemies, werewolves, producing only wolf-like howls. When exhaustive research fails, he captures a live werewolf, Yonaga, for study. Testa protects Yonaga from harm, demonstrating compassion that gradually earns her trust; she eventually reveals her name to him.

During a confrontation with Lance Corporal Balke, Yonaga uses her blood to transform Testa into a werewolf. This transformation grants him enhanced abilities, enabling him to save Alex Rossa, whom he follows out of a sense of debt. He kills Balke but recognizes his werewolf state makes returning to human society impossible. Consequently, he departs with Yonaga, leaving Alex behind.