Gaku

Gaku is a tall and muscular young man with spiky slicked back bluish-grey hair and hot pink eyes adorned with a red eyeliner in the outer corner. He wears a pair of black square-shaped earrings, a high-collared navy blue jacket with a yellow button that loosely falls around his body that is covered in multiple scars with the sleeves rolled up, bandaged hands, navy blue baggy pants and white sneakers with light grey stripes and a black lace (the sneakers are fully white in the manga). He always carries his weapon wrapped in bandanges over a bag in its right arm.

Gaku is shown to be an extremely calm and laidback individual who rarely got agitated or angry, even during fights or life-and-death situations such as when he lost an arm during his encounter with Takamura[5]. He often compared real life to a video game, describing a deadly injury as a "speedrun to death" or describing killing itself as a "game". His nonchalant attitude was shown on multiple occasions, such as when he ate snacks or played video games in the middle of a fight. For instance, he compared fighting against the JJA applicants while controlling Shinaya to playing Resident Evil or even using the restroom after getting blasted through a door.

Besides his extremely casual behavior, Gaku was also be an extremely brutal person to deal with, killing JAA members many times without hesitation or mercy. He disregarded any pain or collateral damage done to Shinaya when he overexerted the man's body while controlling him and was shown to have fun during fights or even when killing a strong opponent, commenting that the action of killing is something you have to enjoy or it's a waste.

Gaku is one of the orphans raised in the Al-Kamar Orphanage along with Uzuki, Kumanomi and several other orphans such as Haruma. After Uzuki managed to free all the orphans from the orphanage, Gaku along with a few of them became part of the X's Organization. When Gaku was still 13, Asaki (then in charge of the Al-Kamar orphanage) would take him hostage as a way to force Uzuki to kill Kindaka and once Uzuki had killed Rion Akao, he managed to free Gaku.

The Japanese Association of Assassins, also known by the abbreviation JAA (殺連, Satsuren?), is an official assassin organization based in Japan. It is the largest of its kind at a member count of 1,000, with just under 400 of those being professional assassins.

Due to the actions of Slur and his group, over a quarter of JAA assassins have been purged.

As the largest assassination organization in Japan, the JAA effectively holds a monopoly over the business. The JAA is described to be an extremely wealthy organization; the JAA Tokyo Bureau is vast and extensive with enough infrastructure to resemble part of a city.

In addition to assassination jobs, the JAA offers a more diverse range of services including weapons manufacturing or repairing public spaces damaged during assassination missions. Clients pay a fee to the JAA for these jobs, who then pass the assignment onto the appropriate individual.

Information is discreetly transmitted to assassins. Examples include highly expensive movie rentals and encoded scratch cards.

The Order is a special group of JAA assassins that, as the name suggests, maintains order in the assassin world whenever friction arises, i.e.: dealing with anything that may prove troublesome for Japan's assassin industry if not dealt with immediately. The Order is made up of the strongest assassins in the JAA and is thus a very small group. Members of the Order are so powerful that the JAA rarely assigns several members to the same mission; having the entire Order sent for one assignment has never been seen.

Kei Uzuki was initially portrayed as a calm and cold man, being able to kill a quarter of the assassins in cold blood without a hint of words. He is also a sadist, considering he almost lack any remorse for his killings and provoked Sakamoto by mentioning his 6-years old daughter when Sakamoto refused to fight with the intention of taking the former's life, hinting that he may harm Sakamoto's family if he were to be left alive.

However, during his groups attack on the JAA, Uzuki showed a friendlier, more caring side which was seen through his conversation with Gaku and the remorse he felt at Uda's self-sacrifice for the others to escape Takamura. As he demonstrated multiple times, Uzuki's cold and deadly personality changes radically whenever he is alone with his friends or those he cares about, showing a softer and friendlier side of him which also seems more vulnerable. Gaku and Uzuki first met at the Al-Kamar orphanage

Kashima is a tall man that wears a pink polo shirt under a magenta business suit and the mask of a realistic reindeer head with a dark brown snout and cream-colored spots in the ears and under his eyes Kashima is cordial, and business-oriented, and emphasizes a man who has polite manners when killing someone or something. He frequently meets his subordinates at casual venues such as karaoke clubs or fast-food joints and allows them to eat or drink on the job as long as it doesn't interfere with their work.

He has a strong fascination with cutting-edge technology, expressing his disdain for standard guns and knives after becoming a cyborg. He seems to take great pride in his augmented body. Kashima is a part of Slur's (Kei Uzuki's) organisation X along with Gaku

Gaku uses a large double handed mace