A 15 year-old teen who gets by robbing rich people's mansions. He's very intelligent and sharp, his strong point being his knowledge of mechanics. He is also a skilled shooter and likes to carry around a gun. Gareki distrusts people and isn't very sociable, stating that he hates associating with others. However, despite his arrogant and distant attitude, he does have a more caring side that he doesn't like showing, seeming to have a soft spot for smaller children and Nai. He originally thought to use Nai for his robbing schemes but later joins him to find Karoku. When Nai tells Gareki about Karoku knowing that they were together, Gareki realizes that Karoku wants to keep him away from Nai.
Gareki has short, messy black hair and black eyes, though they are sometimes shown as gold. He usually wears a pair of goggles on his head and often wears a long red jacket, black pants, and skin tight shirts or tank tops, some with only one strap. He also sometimes wears jumpsuits. He is noted to be quite a handsome young man, though he doesn't seem to care about his appearance much. He looks like a sexgod.
Gareki has had a poor childhood but has also been shown to have very high intelligence. Though he is only 15 years old, he is highly knowledgeable in technological fields. At present, he secretly observing the original machinery structure and systems inside the Circus ships. He also thinks of investigating the Sheep sooner oor later. He likes to read books of practical knowledge that he is interested in and has the habit of falling asleep in the position that he reads.
Gareki does not trust others easily because he grew up in a poor environment. Even as a child he constantly went out by himself. Even when he agrees to become someone's partner, he does it for the sake of fulfilling his own desires and needs. However, he has a soft spot for women and children, especially Nai, and loathes the idea of hurting them. Because he used to be a thief, he is sneaky and clever. He is used to faking smiles and putting on 'good boy' acts. He is uncomfortable at the idea of becoming close to other people, and for a long time did not consider Nai or anyone at the Circus his friends. He also feels strange for thinking that the Circus ship is home.
Eventually he becomes frustrated at his own weaknesses and voluntarily goes to a school which raises recruits for Circus. Yogi, Nai, and Tsukumo gave him gifts, to which he awkwardly accepted. Nai and Yogi yell after him that he has to come back because the Circus ship is his home, causing him to secretly cry in happiness.
Originally, Gareki only considered Nai to be a burden and only got close to him to get his hands on Nai's Circus bracelet. As they spent more time together, Gareki became more fond of Nai and eventually became something akin to a babysitter, mostly because he had the tendency to order Nai to take care of himself more often. He tries to teach the pure Nai about how he has to get his hands dirty sometimes, but he gave up. He becomes fairly overprotective of Nai and is still trying to help him find Karoku.
Gareki didn't really like Yogi at first because the latter was always too friendly, noisy, or just plain irritating. He does, however, acknowledge that Yogi is strong and respects him for it. Yogi tries to act like a big brother to Gareki, like how he acts like a big brother to Nai, but Gareki refuses to let him get close. Gareki was shown to be worried, however, when Yogi was injured during a battle, calling out his name properly for the first time. Eventually, he at least comes to see Yogi as his comrade.