Yonaga is a 16-year-old female werewolf who maintains a primarily human appearance, distinguished by brown hair, European Gray Wolf ears, and a tail. She cannot fully transform into a traditional fanged werewolf form but wields unspecified supernatural powers. Her species is locked in conflict with humanity. Captured by human soldiers after being surrounded in a wooded Siberian area, her apprehension was orchestrated by Allied Cryptanalysis Department agents Testa Lielbelle and Alex Rossa. They sought her unique skills to decipher the enemy's encrypted Luger Code communication system.

While confined in a shed, the location was attacked by other werewolves attempting her rescue. After escaping this assault, she revealed her name, Yonaga, to her captors. She possesses a serious demeanor, though moments of comic relief emerge, such as blushing unexpectedly in tense interactions. An unlikely bond forms with Testa and Rossa, particularly after Testa intervenes to save Rossa from a larger werewolf threat, revealing unexpected werewolf traits himself during the clash. Her core role revolves around the decryption efforts and the shifting dynamic between her human captors and her own kind.

Her known involvement is strictly confined to the events of her Siberian capture, the subsequent shed attack, and the immediate aftermath. The documented media explores no further development or expanded backstory beyond these occurrences.