Hayato Gokudera is a fictional character introduced as a transfer student in Tsunayoshi Sawada's class who quickly becomes one of the protagonist's first friends and most loyal allies. Born in Italy, Gokudera is of mixed heritage, being three-quarters Italian and one-quarter Japanese, with his mother being of Japanese descent. His distinctive appearance features mid-length silver-grey hair, often parted in the middle, and narrow green eyes. His hairstyle is noted to be a copy of his mentor, Dr. Shamal. He typically wears the Namimori Middle School uniform along with various accessories such as wristbands and belts, and in the manga adaptation is frequently depicted as a chain smoker, a trait that was removed for the anime version.

The character's background is marked by tragedy. As a child, he was a talented pianist, an ability inherited from his mother, who was a gifted musician. His mother was the lover of his father, who was already part of a mafia family with a wife and daughter, Bianchi. Because illegitimate children were not tolerated in the mafia world, everyone was told that Gokudera was also Bianchi's mother's child. His real mother died in a car accident while on her way to visit him, an incident that young Gokudera initially believed was caused deliberately by members of his father's organization. Later revelations suggest his mother was already suffering from an illness at the time of the crash. After discovering the truth about his mother's death at the age of eight, he fled the family mansion and eventually decided to join the mafia, seeking revenge against his father. Due to his status as an oriental half-breed, many families refused to accept him, but he was eventually taken in by the Vongola Family, where he worked as a hitman and earned the nickname Hurricane Bomb Hayato. He sought out Dr. Shamal, who taught him how to use dynamite as his primary weapon.

In terms of personality, Gokudera is hot-tempered and irritable toward almost everyone except Tsuna Sawada. He cultivates the image of a rebellious bad boy, a persona that makes him extremely popular with the female students at school. Despite his delinquent appearance and hostile attitude, he is surprisingly intelligent and excels academically, consistently acing his tests and demonstrating a methodical, calculating approach to problem-solving and combat. He has a pronounced obsession with cryptozoology and the supernatural, believing in unidentified mysterious animals and extraterrestrials, and is a devoted reader of magazines about the wonders and mysteries of the world. Due to a traumatic childhood experience involving his half-sister Bianchi's cooking, seeing her face causes him to experience severe stomach pain and collapse, though he is immune when she wears something that covers part of her face.

Gokudera's primary motivation is to become Tsuna's right-hand man, a role he takes with utmost seriousness. He is fiercely loyal to Tsuna, who was the first person to open his heart and the one who saved him from his own explosives when they first met. This devotion borders on idolatry, as he refers to Tsuna exclusively as Tenth, and he tends to view most of Tsuna's other friends, particularly Takeshi Yamamoto, as rivals for the position of closest ally. Over time, however, he begins to develop friendlier relationships with the other guardians, though he is too embarrassed to admit it openly.

His role in the story is that of the Vongola Storm Guardian, one of Tsuna's six elemental guardians. As the Storm Guardian, his flame attribute has the property of disintegration, which allows his attacks to break down whatever they touch. He is often at the forefront of battles, using his intelligence and explosive arsenal to protect Tsuna and defeat enemies. Throughout the series, he appears in all major story arcs, including the Kokuyo Arc where he is ranked the third strongest student at Namimori Middle School, the Varia Arc where he battles the天才 assassin Belphegor for the Storm Ring, and the Future Arc where he plays a crucial role in deciphering messages left by his future self and developing new combat techniques.

Key relationships shape his character development significantly. His bond with Tsuna is the most important, as Tsuna's influence gradually teaches him to value his own life rather than recklessly throwing it away in battle. His relationship with his half-sister Bianchi is complicated by his physical reaction to her face, though she cares for him and later helps train him. He has a one-sided rivalry with Takeshi Yamamoto, whom he initially despises but eventually learns to respect and cooperate with. He also has little patience for the young Lambo and is frequently annoyed by Haru Miura, though he demonstrates moments of genuine concern for them in dangerous situations.

Throughout the series, Gokudera undergoes notable development. He starts as a lone wolf willing to die for Tsuna without regard for himself, but gradually learns the value of teamwork and his own life. His strict declaration that anyone older than him is an enemy softens over time as he learns to work with older allies like Dino and Lal Mirch. He also matures from a hotheaded novice into a capable strategist and teacher, as seen when he instructs the younger versions of Ryohei and Lambo in using their box weapons.

Regarding his notable abilities, Gokudera is a specialist in the use of dynamite, carrying large quantities concealed on his body at all times. He has developed numerous techniques including Double Bombs, Triple Bombs, Rocket Bombs that use mini thrusters for homing capabilities, and smoke bombs for creating diversions. His combat style is methodical and calculated, often setting traps and using optical illusions with differently sized explosives to deceive opponents. He is a mid-range fighter who excels in enclosed spaces where he can maximize the effectiveness of his explosives.

His abilities expand significantly with the introduction of box weapons and the Dying Will Flame system. Gokudera is unusually gifted in that he can generate five different types of Dying Will Flames: Storm, Lightning, Rain, Cloud, and Sun, though Storm is his primary and strongest attribute. This allows him to utilize the Sistema C.A.I., or Instantaneous Arms Change System, a complex arrangement of box weapons that his future self invented. The system includes the Flame Arrow, a skull-shaped cannon mounted on his arm, and four skull rings representing different flame attributes. Different combinations of rings produce different types of attacks, such as the Flame Thunder which fires a solid beam of Storm and Lightning Flames, or the Gatling Arrow which fires four simultaneous Storm arrows.

His animal box weapon is a storm cat named Uri, which takes the form of a small, disrespectful cub that frequently scratches him. When infused with Sun Flames, Uri transforms into a massive leopard called Pantera Tempesta. After receiving the Vongola Box upgrade, Uri can perform Cambio Forma to become G's Archery, a large ornate bow made of bones and Storm Flames that serves as Gokudera's ultimate weapon. He also possesses a motorcycle that he learns to ride with proficiency, making him the first guardian to master this vehicle.