Puck is a small elf of the pisky race, a people descended from the ancient spirits of wind. He is the first companion to travel with Guts after the Eclipse, joining the protagonist during his early days as the Black Swordsman. Originally a resident of Elfhelm, an idyllic elf homeland, Puck left out of sheer boredom and soon found himself in trouble, only to be rescued by Guts. Although Guts repeatedly tried to rid himself of the tiny creature, Puck decided to stay by his side, beginning one of the most enduring partnerships in the story.

In appearance, Puck is a palm-sized humanoid with pointed ears, insect-like wings, and a head of blue hair, with the same blue-green coloring in his large eyes. His design is often exaggerated into a rounded, chestnut-like chibi form, which suits his comedic presence. He is frequently seen carrying a burdock leaf as his closest thing to a weapon.

Puck's personality is defined by a whimsical, hyperactive, and light-hearted nature that stands in sharp contrast to the grim and violent world around him. He is talkative, mischievous, and prone to playful antics, exaggerated impressions, and constant commentary, often mocking Guts' hygiene or attitude. Beneath this comedic surface, however, he is genuinely perceptive and empathetic. Rather than judging people by their harsh exteriors, Puck prefers to look for the inherent good in those he meets, and he shows remarkable patience, even tolerating Guts' early verbal and physical abuse. When the situation turns serious, Puck abandons his joking demeanor and acts with sincerity, courage, and moral clarity. He is quick to befriend innocent figures such as Jill, listening to their tragic stories with genuine compassion, and he will openly rebuke Guts when he believes the swordsman is being unnecessarily cruel, as he does during the Lost Children arc. Elves are noted for having a strong sense of duty, and Puck's empathic nature is part of that heritage. On occasion, his behavior even suggests an awareness of the fourth wall.

His motivations center on supporting Guts and remaining loyal to him despite the overwhelming dangers they face. Puck understands that he is far outmatched by the demons and apostles that Guts battles, yet he consistently chooses to act alongside his companion rather than flee. He also seeks adventure and enjoyment in their travels, maintaining a playful curiosity that keeps a thread of lightness alive even in the darkest moments. Narratively, he serves as both comic relief and an emotional anchor. He functions as a witness and catalyst for Guts' humanity, questioning the swordsman's decisions, offering comfort, and gently helping to pull him back from total despair and rage. Without his presence, Guts' journey would be considerably bleaker.

Puck's role changes over the course of the story. In the earlier arcs, he frequently acts as a moral counterweight, scolding Guts for his callous treatment of others and trying to steer him toward compassion. Over time, as Guts slowly regains trust in people and begins to open up to companions such as Farnese and Isidro, Puck's lecturing fades and his presence becomes primarily a source of levity and steadfast support. His loyalty never wavers, and even when the two briefly part ways over Guts' brutality, Puck always returns because he sees the good within him.

Among his key relationships, his bond with Guts is the most significant, marked by mutual dependence in different ways: Guts offers protection and strength, while Puck offers warmth, healing, and moral grounding. With the young Isidro, Puck shares a close friendship and acts as a self-appointed mentor, often sitting on the boy's head and comically boasting of his nonexistent combat mastery, including attempts to teach his invented fighting style. With Ivalera, a fellow elf and companion, he has a bickering, rivalrous dynamic, since she is far more serious and composed than he is, though he tries to convince her they are alike. His interactions with gentle characters like Jill highlight his empathetic side.

Puck possesses several notable abilities. The powder from his wings has healing properties that can close wounds and aid recovery during battles, making him a valuable support for Guts. He can emit a bright flash of light from his body that temporarily blinds enemies, useful for distractions and surprise openings, and he can launch painful spiny projectiles in an attack known as the Bloody Needle, which stings without being fatal. He is also capable of flight and frequently adopts exaggerated costumes and personas for comedic effect or to distract opponents. His physical size and strength are severely limited in direct combat, so he relies on speed, cleverness, and misdirection rather than brute force. Overall, Puck develops from a seemingly simple comic figure into a loyal, emotionally vital companion whose humor and empathy help preserve the humanity of everyone around him.