Jiisuri (designated G3A3) is a West German battle rifle chambered in 7.62x51mm NATO. She attends Seishou Academy as a high school student alongside classmates like Fal and Ichiyon, belonging to the battle rifle class. Though outwardly disciplined and strict, she possesses a fundamentally caring and friendly personality. This kindness manifests as an older sister figure to numerous younger sisters in the submachine gun class, including HK33E and MP5 variants, reflecting their shared Heckler & Koch firearm lineage.

She ranks among the academy's top snipers due to exceptional long-range marksmanship. This proficiency sparks a notable rivalry with Sig, another skilled sniper from the middle school assault rifle class, which evolves into mutual interest during their engagements. Jiisuri utilizes a distinctive recoil-reduction shooting posture effective in combat, though its unconventional and compromising appearance causes her personal embarrassment.

Her physical characteristics include black hair and yellow eyes, frequently paired with dark pantyhose. She shares a strong familial resemblance with her many younger sisters, consistent with the design lineage of Heckler & Koch firearms derived from the G3 platform. Her established role and relationships within the main narrative define her character.