The Kokuyo Junior High Gang is led by Rokudo Mukuro and created after he broke out of prison. The group consists of the people who escaped from prison with the possessed Mukuro. They are:
Mukuro Rokudo established this group in order to find Vongola the 10th to execute his plan of world destruction. Mukuro planned on engulfing the world with darkness, disaster, and war. In order for his plan to work, he needed experience and tried to destroy something smaller than the world, the Mafia. He planned to take control of Tsuna and use Vongola's power to destroy the Mafia. This idea also applied to his plan of destroying the world, take control of the world's greatest leaders, and start a World War. The group was formed to protect their plan of destruction and make it possible to achieve the goal. Their plan is foiled when Tsuna awakens and wins the duel against Mukuro. All the escapees are sent back to prison (at least the ones that were still alive). Eventually Ken and Chikusa escape with the help of Mukuro in order to help Vongola and protect Chrome Dukuro. Mukuro is sent back to prison and remains there.
Ken and Chikusa is part of the family, Estarneo family, the same exact family that created the Possession Bullet. After the Possession Bullet became Forbidden, the Estarneo Family began testing on their children (treating them as "guinea pigs"), in order to survive. Ken, Chikusa, and the other children endured the tests, until Mukuro saves them. Ever since that day, Ken and Chikusa , and all three of them grew up together. Ken uses teeth cartridges of animals in order to take on their characteristics and fighting abilities, while Chikusa uses yo-yos to fight and when the yo-yo is in range of an opponent, it launches several needle-like spires at the opponent
Birds is a cruel, dirty old man that cares and nurtures birds. In return, they follow every command of his. He uses his birds to watch others and listen to their conversations. He blackmails Tsuna in order to prevent them from reaching Mukuro. He enjoys watching people in pain and confused. He is not a large physical threat; however by using blackmail, he can manipulate people and force them to do unspeakable things.
Lanchia was once homeless, and a family brought him in and raised him. In return, he rose and became a guard, and is called the strongest man in Northern Italy. He cared for Mukuro Rokudo when his family took him under their wing and raised him, just as they did with himself. In return, Mukuro possesses him and kills off the entire family. He is sent to prison for Mukuro's actions and acts as a double in order for Mukuro to remain safe and in hiding. He possesses a large metal ball (mace-like weapon) with snake shaped carvings in it to pull his opponents in front of the ball. He has a good heart and Tsuna sees this in their fight.
Very popular serial killers that uses stealth to sneak up on their prey and "slice" them up. They were sent to kill Haru and Kyoko if Tsuna and Friends did not agree with Birds' terms. They both use their abnormally long fingernails as weapons to slice.
The only girl in the group. She uses her Clarinet as a weapon in battle. With her Clarinet, she can make microwaves to fry, detonate, and destroy her opponents body. She is self-centered and only cares about her self and her money. She, like Lanchia, is also well versed in hand to hand combat.