Gieve is a character who appears exclusively in the Fugitive Arc of the World Trigger anime, serving as the primary antagonist of that storyline. He is a humanoid Trion Soldier, an artificial being created from trion, the energy source that forms the basis of the series' combat and technology. More specifically, Gieve is a prototype created by a scientist named Dr. Lamia from the chaotic nation of Ergates. He is considered a failure, a prototype who came before another creation named Lilith. Gieve is sent to Meeden, the world where the main story takes place, on a mission to retrieve Lilith, who has escaped Ergates alongside a genius engineer named Xeno.

In terms of appearance, Gieve is presented as a young man with blonde hair that reaches his shoulders and striking yellow eyes. He typically displays a calm and collected demeanor, often appearing cool and in control of the situation. However, this surface-level composure contrasts sharply with a deeply volatile and obsessive personality. Underneath, he is prone to strong outbursts of emotion, particularly anger. He is shown to despise Xeno with a fierce and personal hatred, becoming fixated on him to the point of obsession and even losing his mind during their confrontations. This rage appears to stem from implanted memories, as Xeno himself has no recollection of Gieve or their supposed past. This disconnect is a source of further torment for Gieve, who interprets Xeno's lack of recognition as a deliberate slight. He worships Lilith, referring to her as the beloved "goddess of destruction" of Ergates and is willing to go to any lengths to bring her back. His relationship with his creator, Dr. Lamia, is more complex; he is shown to have been fond of her and seems to harbor deeper feelings for her, possibly romantic in nature, and he does not seem to resent her for considering him a failure.

Gieve's primary role in the story is that of a relentless pursuer. He tracks Xeno and Lilith to Meeden, engaging in multiple battles with the main characters, particularly the members of Tamakoma Second, who become entangled in the conflict. His motivations are driven by a mixture of his programmed mission and his deeply personal, seemingly manufactured vendetta against Xeno. As the arc progresses, Gieve's role evolves from a seemingly straightforward villain to a more tragic figure. His world is shattered when his own companion, an autonomous Trion Soldier named Charon, reveals that Gieve himself is being used as a pawn. He learns that his memories are false constructs and that he is just as much a disposable tool as the Trion Soldiers he commands. This realization triggers a violent breakdown and a desperate, monstrous transformation as he absorbs massive amounts of trion, eventually leading to his self-destruction.

As a combatant, Gieve is highly formidable. He fights using a trigger on his left arm, which is similar to Xeno's device, allowing him to summon various Trion Soldiers from specialized capsules to do his bidding. He is also a capable hand-to-hand combatant, wielding a blade similar to a Scorpion to fight directly when needed. While he can sometimes be outmaneuvered by clever tactics, his skills are genuine, as he is noted to be a decorated operative who has earned national medals in his home country. His most notable ability, however, is that he is a Black Trigger user. The Black Trigger he wields originally belonged to Dr. Lamia and enhances his ability to control his Trion warriors, granting them increased power, speed, and combat capabilities. In this enhanced state, he is able to overwhelm powerful Border agents and fight on par with Yuma, who himself is a Black Trigger user. Ultimately, Gieve's development is a tragic arc of a created being who, manipulated by false memories and betrayed by those he trusted, falls from a position of a threatening, composed hunter to a pitiful, broken weapon that is consumed by its own power and despair.