Byakuran is the former boss of the Gesso Famiglia and the former leader of the Millefiore Famiglia, a powerful criminal syndicate formed by the merger of his own group and the Giglio Nero Famiglia. He is the primary antagonist of the future arc, serving as a formidable adversary to the Vongola Family.

In terms of background, Byakuran was once an ordinary young man who felt a profound sense of boredom with the world around him. His life changed when he met Shoichi Irie, who had been experimenting with the Ten Year Bazooka. By encountering two different future versions of Byakuran through Shoichi's time travel, the so-called "Phalaenopsis paradox" was created, which shattered the barriers between parallel worlds and awakened Byakuran's unique and extraordinary ability. With this power, he began conquering parallel worlds and was eventually chosen by the Cervello to be the rightful holder of the Sky Mare Ring, solidifying his path to become a dominant force in the mafia world.

Personality-wise, Byakuran is a complex figure. In his future role as the Millefiore boss, he presents a deceptively cheerful and carefree demeanor, especially towards his close friend Shoichi Irie. However, this pleasant facade hides a ruthless, cruel, and ambitious nature. He is willing to sacrifice anyone, including his own subordinates or innocent people, to achieve his goals, viewing others as mere pawns or toys for his amusement. Once he loses interest in a person, he has no hesitation in ordering their death. Yet, this is not his complete nature. He is also portrayed as someone who was not attached to anything, and his relentless conquest was a way to escape an inner emptiness. This changes in the present timeline following his future self's defeat, where he retains his easygoing personality but undergoes significant development, becoming more loyal and caring, particularly towards Uni.

His primary motivation in the future is to obtain ultimate power. He seeks to collect the complete Tri-ni-set, which comprises the Vongola Rings, the Mare Rings, and the Arcobaleno Pacifiers. He believes that uniting these three artifacts will grant him godlike, limitless power. To this end, he orchestrates the near-total extermination of the Vongola Family in his timeline and even releases a special radiation to kill all the Arcobaleno.

In the story, Byakuran is the driving force behind the central conflict of the future arc. After his subordinate Shoichi Irie betrays him and allies with the Vongola, Byakuran reveals that he foresaw this treachery. He then escalates the conflict by introducing his true elite guard, the Real Six Funeral Wreaths, and challenges the Vongola to a realistic version of a strategy game called "Choice". He serves as the final boss, confronting Tsunayoshi Sawada directly in a climactic battle after his most powerful pawn, Ghost, is defeated. After his defeat in the future, the Byakuran of the present timeline appears in later arcs, such as the Inheritance Ceremony and the Curse of the Rainbow arc, where he acts as an uneasy ally to Tsuna and fights as a representative for Uni.

Key relationships define much of his character arc. His bond with Shoichi Irie is foundational; Shoichi is the one who inadvertently awakened his power and was considered his best friend, even though Byakuran anticipated his betrayal. His relationship with Uni is particularly significant. In the future, he views her as a tool, drugging her to become a figurehead and referring to her as the "final piece" needed for his plan. Her subsequent sacrifice enrages him, as he sees it as his "toy" being broken. However, in the present timeline, her genuine kindness saves him from the loneliness and emptiness he felt after achieving his goals in a nightmare vision. This act allows him to be "reborn," leading him to become one of her most devoted protectors. His relationship with Tsunayoshi Sawada also evolves from that of a ruthless enemy who finds him a worthy opponent to a friendly rival and ally. He views his Real Six Funeral Wreaths as pawns in the future, discarding them without remorse, but in the present he genuinely cares for them.

Byakuran undergoes a notable character development from the future to the present. The future Byakuran is a tyrannical conqueror who meets his end at Tsuna's hands, an outcome that erases his evil deeds across parallel worlds. The present Byakuran, having witnessed this potential future and been saved from his own hollow nature by Uni's warmth, changes his path. He abandons his quest for ultimate power and instead dedicates himself to protecting Uni and even cooperating with his former enemies, demonstrating genuine care and loyalty.

His notable abilities are both powerful and unique. His signature power is his ability to communicate with and share knowledge, experiences, and abilities with all his other selves across parallel universes. This gives him nigh-omniscient tactical knowledge and allows him to learn from countless alternate timelines, though extensive use of this power can weaken him significantly. He is the wielder of the Sky Mare Ring, which allows him to generate powerful flame-based attacks. His combat techniques include White Point, a concentrated flame projectile from his fingertip; White Clap, which can extinguish an enemy's Dying Will Flame with sheer pressure; White Grasp, which creates a giant hand to crush opponents; and the Jet Cannon, a powerful propulsion attack reminiscent of Tsuna's X Burner. He can also manifest large wings made of Dying Will Flames, which start as white but can transform into black wings that represent his true power and can be used for propulsion and attack. His Box Weapon is a White Dragon that can fly at high speeds. He also commands a terrifying doppelganger named Ghost, a version of himself from another parallel world. Ghost is a massive, slow-moving entity with no self-awareness that absorbs the Dying Will Flames of anyone nearby, and all the power Ghost absorbs is transferred directly to Byakuran, making him exponentially stronger.