Shuichi Iguchi has a distinctive, reptilian appearance, with bright green, scaly skin and a face resembling that of a lizard. His hair is long, swept back, and colored a faded pinkish-purple, contrasting sharply with his green complexion.

Inspired by his idol, Stain, Spinner models his outfit after the Hero Killer’s, wearing a sleeveless shirt, dark baggy pants with brown holsters, black boots, and pale metal knee guards. He wraps his arms in bandages and sports a red scarf, a white tattered face mask, and goggles on his forehead. Spinner also carries an enormous sword made from smaller blades bound together, a signature weapon that was later destroyed and replaced with a single large blade.

During the Final War, after being granted the Body Bulk Quirk by All For One, Spinner’s body mutates drastically. He grows several stories tall, becomes extremely muscular, and his scales darken. His appearance and behavior turn increasingly beast like. Following the war, Spinner is left heavily scarred across his face and neck, his scales torn and damaged from the strain of using multiple Quirks. In his everyday life, he now dresses simply, often wearing a light blue hoodie under a black leather jacket.

Shuichi Iguchi harbors deep resentment toward heroes, viewing them as corrupt and hypocritical. His contempt is made clear when he cruelly steps on Pixie Bob’s unconscious body after defeating her alongside Magne. Like Dabi, he reveres Stain, though his admiration borders on obsession. Spinner not only shares Stain’s ideals but imitates his fighting style, clothing, and weaponry, striving to fulfill his idol’s vision of true heroism. This devotion makes him one of the more morally conscious members of the League of Villains, as shown when he defends Izuku Midoriya, whom Stain deemed a true hero, and questions whether the League’s actions truly align with Stain’s teachings.

A victim of lifelong discrimination for his Mutant Quirk, Spinner often shows surprise and humility when others compliment his appearance. Despite his villainous path, he displays moments of empathy and doubt, particularly when learning that Tomura Shigaraki’s goal is to destroy society rather than reform it. Although Spinner initially followed Stain’s ideology, he gradually shifts his loyalty to Tomura, acknowledging his own weakness but accepting it as part of his purpose.

Spinner deeply values his comrades in the League, considering them true friends. He bonds with Tomura over video games and shows care toward members like Himiko Toga, urging her to return safely during battle. His dedication to Tomura is unwavering, even as All For One begins exerting control over the League, Spinner chooses to remain loyal to Tomura, guarding him and expressing concern during his transformation.

In the end, Spinner finds hollow comfort in the fleeting admiration he receives, returning to his core motivation, doing everything for Tomura’s sake. When Izuku Midoriya visits him after the Final War, Spinner initially lashes out in grief, blaming him for Tomura’s death. However, upon hearing Tomura’s final message, Spinner breaks down, mourning his lost friend and hero. Moved by Izuku’s words, he resolves to write a book preserving the League of Villains’ legacy, ensuring their story and Tomura’s memory will not be forgotten.

Spinner is a skilled close-quarters fighter who relies on his arsenal of bladed weapons. During the Vanguard Action Squad invasion, he fought Mandalay on even ground, showing notable agility and precision until Izuku Midoriya intervened and destroyed his weapon. Despite being defeated, Spinner’s quick reactions and ability to read his opponents demonstrated his solid combat instincts. His determination and loyalty to his comrades made him a reliable member of the League of Villains.

As part of the Paranormal Liberation Front, Spinner showcased both endurance and adaptability in battle. He fought through waves of Meta Liberation Army soldiers, standing his ground even when outnumbered. After receiving the Body Bulk and Scalemail Quirks from All For One, Spinner’s strength and durability greatly increased, allowing him to crush concrete and withstand powerful attacks. However, the added Quirks also took a toll on his mind, leaving him more unstable and beast-like during the Final War.

Despite his monstrous appearance and growing instability, Spinner maintained his loyalty to Tomura Shigaraki and his resolve to see his mission through. His enhanced strength, agility, and resilience made him a formidable opponent, while his tactical awareness allowed him to quickly adapt to chaotic situations. Even after his defeat, Spinner proved to be more than just muscle—his drive and conviction made him a symbol for others who had been cast aside by society.