Grewishka is a formidable and brutal cyborg antagonist who serves as a primary enforcer for Nova, the mysterious and god-like ruler of the sky city of Zalem. His origins are rooted in the scrapyards beneath Iron City, where he was discovered and salvaged by Nova. This act of being rebuilt and given a purpose created a deep, almost fanatical sense of loyalty in Grewishka, who sees Nova as his master and the sole source of meaning in his existence. Physically imposing at around nine feet tall, his massive cybernetic body is a weapon in itself, designed for destruction and intimidation.

The personality of Grewishka is defined by sadism, cruelty, and a deep-seated bloodlust. He is not merely a mindless killer but takes genuine pleasure in the suffering of others. He taunts his opponents with demeaning nicknames, referring to Alita as "Little Flea," and sadistically fantasizes about turning her into a living pendant to adorn his chest so he can listen to her plead for mercy. This cruelty is not without a twisted sense of pride, as he states that "Grewishka does not forget," holding a long and vengeful memory for those who have wronged him. Despite his monstrous exterior and actions, there is a tragic dimension to his character. He is portrayed as being unable to comprehend a life outside of Nova's control, seeing himself as worthless trash who exists only to be a weapon. He is Alita’s dark mirror, representing what she might have become if she had been found and raised by a malevolent force like Nova instead of the caring Dr. Ido. After Alita punches out his eye, he even refuses to have it repaired, claiming he wants to feel the pain, which hints at a masochistic streak as well.

Grewishka's primary motivation is his devotion to Nova, and his overriding goal is to destroy Alita. After being humiliated and losing an arm in their first encounter, his quest for revenge becomes his sole reason for living. His role in the story is that of a relentless physical threat and a recurring obstacle designed to test Alita's strength and resolve. He serves as a direct link to the larger, unseen threat of Nova, embodying the brutal power that Zalem can wield over Iron City. His presence forces Alita to confront not only a powerful enemy but also the darker potential within herself.

His key relationships are defined by servitude and rivalry. He is utterly subservient to Nova, bowing to him and following his commands without question. Vector acts as a handler and intermediary for Nova, though Grewishka's loyalty is to his master alone, not to Vector. Chiren, a cybernetic expert, is the one who repairs and upgrades his body, but he ultimately murders her when she tries to leave Nova's service. His most significant relationship is with Alita, whom he views as a challenge, a pest to be eliminated, and an obsession. She is his polar opposite and rival.

The character undergoes a distinct development in terms of power and desperation. Initially, he is a confident and terrifying predator who toys with his prey. After his first defeat, he returns to Chiren to be rebuilt, receiving significant upgrades that grant him new abilities, making him far more resilient and deadly. In this enhanced state, he is able to overwhelm and nearly destroy Alita, chopping her body to pieces. However, by their final confrontation, the dynamic has shifted. Alita has embraced her true power as a warrior from Mars and wields the Damascus Blade. In this last battle, Grewishka is no longer a match for her. He is easily outmaneuvered and killed, being sliced in half, a moment that signifies the protagonist's final victory over her most persistent physical foe.

Grewishka possesses several notable abilities that make him a terrifying opponent. His primary assets are his immense strength and formidable resilience, as his cyborg body is built to be incredibly sturdy. His signature weapon is his hands, which are equipped with "grind-cutters." These are extendable, bladed fingers that can transform into long, razor-sharp tendrils capable of cutting through other cyborgs with ease. He uses these to slice Alita into several pieces during their second fight. After his upgrade, his durability is greatly enhanced, allowing him to shrug off attacks that previously wounded him. Despite his size and power, his main weaknesses are his arrogance and his status as a large, predictable target. In his final moments, Alita exploits this, dodging his attacks with ease before landing a killing blow.