Hayato Gokudera is a half-Italian, half-Japanese teenager first encountered as a rebellious Italian transfer student. His silver hair, green eyes, and distinctive non-standard school uniform featuring accessories like wristbands and poison-detecting silver pieces mark his appearance. These accessories specifically counter his half-sister Bianchi's toxic cooking, stemming from childhood trauma causing severe reactions to her uncovered face, sometimes leading to unconsciousness.

Born into mafia circles as the illegitimate son of a mafia figurehead, his mother—a talented pianist—died under suspicious circumstances officially termed a car accident while delivering a gift to him; this event, later suggested to involve deliberate sabotage by his father's organization, prompted him to flee home at age eight. Rejected by multiple mafia families due to his mixed heritage and musical association, he eventually sought explosives training under Dr. Shamal, adopting dynamite as his signature weapon and earning the nicknames "Smokin' Bomb Hayato" or "Hurricane Bomb Hayato." Despite a turbulent upbringing, he excelled academically through private tutoring and displayed exceptional piano skills cultivated by his mother, though he abandoned the instrument after enduring Bianchi's poison-laced cooking during recitals.

Gokudera's personality blends fierce loyalty with a volatile temper. He idolizes Tsunayoshi Sawada, considering himself Tsuna's right-hand man and protector after Tsuna saved him from his own explosives during their initial meeting. This devotion manifests as extreme protectiveness, though he initially resents others interacting with Tsuna, particularly viewing Takeshi Yamamoto as a rival. He gradually learns cooperation and values the guardian team, while retaining irritability toward figures like Lambo or Ryohei Sasagawa. He possesses high intelligence, superstition, and a fascination with cryptozoology and extraterrestrial phenomena, regularly reading "The Wonders and Mysteries of the World" magazine. Character development shows progression from self-sacrificial recklessness to strategic reliance on allies, prioritizing team safety over personal ambition during the Varia arc after Tsuna emphasizes their collective purpose; later arcs highlight his leadership in coordinating guardians during battles.

As the Vongola Family's Storm Guardian, Gokudera specializes in mid-to-long-range combat using dynamite and complex flame-based systems. His techniques evolve from basic explosives like Double Bombs to advanced strategies involving Mini Bombs for optical illusions or Speed Bombs for propulsion. In future arcs, he masters the Sistema C.A.I. (Instantaneous Arms Change System), wielding five flame attributes via skull-shaped rings: Storm (degeneration), Rain (weakening), Lightning (solid beams), Cloud (propagation), and Sun (acceleration). His Box Weapon, the storm cat Uri, merges with the Flame Arrow to form the Cambio Forma "G's Archery"—a bone-structured bow amplifying his Storm Flames. This system reflects his analytical prowess, demonstrated by decoding his future self's notes and independently completing the C.A.I.'s development.

Gokudera's relationships underscore his growth. While initially antagonistic toward Yamamoto, he gradually accepts him as a comrade after recognizing his own shortcomings. His dynamic with Bianchi remains strained but shifts toward reluctant collaboration during joint training. Though dismissive of Lambo and Ryohei early on, he risks his life to protect them in critical battles like the Varia ring matches. His loyalty to Tsuna remains absolute, driving him to endure severe injuries during conflicts such as the Shimon Family attack, where he acquires the Vongola Storm Gear after his ring is destroyed.