The Grosspoliner is a mystical, sentient sword that appears in the Silent Möbius series. It is a living weapon of tremendous power, originally wielded by the powerful sorcerer Gigelf Liqueur and later inherited by his daughter, Katsumi Liqueur. Prior to Katsumi discovering it, the sword was locked away inside a memorial by the Lucifer Hawks, who sought to prevent her from obtaining its power. The sword only breaks free from its imprisonment upon receiving a sample of her blood, signifying its acceptance of her as its new master.

As a weapon, the Grosspoliner possesses a distinct personality and a high degree of self-awareness. It is several hundred years old and holds long memories, including of the time before the world was ravaged by the failed Project Gaia. This age grants it a philosophical perspective, and it often makes remarks on the state of the contemporary world, sometimes expressing sadness or a sense of fear about how greatly things have changed since its imprisonment. The sword also has a silly sense of humor and is known to snark at its wielder, Katsumi. Its personality was developed more fully in the television series adaptation than in the original manga.

In the story, the Grosspoliner serves as a powerful conduit for Katsumi's magical abilities, allowing her to unleash devastating spells against the Lucifer Hawks. It also acts as an advisor and guardian, providing her with counsel, warning her of danger, and fighting alongside her. As an empathic weapon, it is implied that only a chosen individual, such as Katsumi, can truly wield its power. While originally wielded by her father, Gigelf, Katsumi ultimately surpasses his abilities when using the sword, an achievement potentially linked to the sorcerous abilities inherited from her mother, Fuyuka. Among its notable abilities, the Grosspoliner is described as a living sword capable of retracting its blade and emitting magic energy cutters that can destroy most Lucifer Hawks in a single strike.