Byakuran Gesso (白蘭) is the main villain in the Future Arc of Katekyo Hitman Reborn.
One boss of the Millefiore family during the future arc. He is originally the boss of the up and coming Gesso Family. He appears to insist that his subordinates call him by his name. His name means "White Orchid". Thus far he is shown to be in charge, however he may be taking orders from Uni behind the scenes.
He is extremely ruthless in his goals and has nearly exterminated the Vongola Family. He has not only targeted the Vongola family but all of their allies as well. Byakuran has also ordered that not only members of the Vongola Family be killed, but all of their family members, their friends, and everyone who would help them; this is known as his "killing sweep." Takeshi's father was one of the first to fall in this manner. Byakuran is in the middle of expanding his "killing sweep" to include even more people.
Byakuran has Irie Shoichi to thank for his incredible powers. This is because Shoichi came into possession with the ten year bazooka and was sent into the future where he saw that his life was not what he had wanted it to be. So when he returned to the present he changed his life around and went into the future again to see if he had changed things around. However the first time he went into the future he ran into Byakuran who was a fellow student at the college he was at, and this second time he went into the future he ran into him again. When Shoichi touched Byakuran this second time he gained all the knowledge of the alternate universe that Shoichi had gone to the first time. His knowledge started expanding, gaining the intellect and knowledge of every alternative reality in existence, learning secrets and long forgotten technologies and other information that helped him gain incredible power and take over the world in every single universe he existed in.
Byakuran recieves the Mallefiore Rings he had been waiting for
But he didn't do this with the knowledge alone, he waited until the time was right, he waited for the controllers and watchers of the mafia world to bring him The Millefiore Family rings which granted him incredible power. When this happened he told them that he knew something was coming, and that something was going to take him out of his boring normal life, something that must have come from his knowledge of his success and power in other universes. From here he began bringing his family together, he created the Six Funeral Wreaths, built his base, uncovered the Box Weapons, and started to hunt down every member of the Vongola Family, knowing that they were the only possible risk to him because of his knowledge of alternative universes. However, the Byakuran that we see in the series is different because he is the last Byakuran from any universe to not yet fully take over the world, meaning it is the last hope Tsuna and his family have of stopping him in.
It has recently been revealed that Byakuran has gathered great amounts of information about Tsuna and his family from the past. He has Shoichi Irie researching time travel by analyzing the ten-year bazooka. His plan is to travel to the past to take the Vongola Rings from Tsuna, as they were destroyed in his timeline by the adult Tsuna.
Byakuran wears the Milefiore ring with outstretched wings, identifying it as the most powerful of the rings. He later battles with Mukuro Rokudo, who was posing as Leonardo Lippi, Byakuran's would-be new subordinate. He was far more than Mukuro could handle in battle, and uses a currently unknown attack that Mukuro was trying to learn about. He has purposefully hidden what he is capable of in order to gain the upper hand in the war. The final outcome of the battle is unknown, however Byakuran had no use for Mukuro as he did not have a Vongola Ring and their battle in the chapter ended with him about to strike. He later appears and tells Irie Shouichi of the spy (Mukuro) and that he was taken care of. He also warns of the high probability of an upcoming Vongola attack.
After Uni and Gamma were sacrificed, both Tsuna and Byakuran were enraged, Tsuna's dying will flames came to their highest power it had ever used,with a single X-burner after the power charge, Tsuna killed Byakuran by burning him .