At the beginning of the story, Yuuichi appears to be a diligent and happy student, who works hard to be able to join his friends on the school field trip. He values his friends heavily throughout the story. He shows kindness and a willingness to self-sacrifice for the sake of his friends, even going so far as to brand himself the traitor in order to prevent further discord. As the story progresses and the games become more and more serious, however, Yuuichi begins to show a much more sinister side. This dark nature is likely the result of his troubled upbringing by an adopted mother who had to sell her body and a con man/swindler who served as a father figure and teacher. He shows little remorse for any of his more devious actions and appears sadistic at points when he takes pleasure in the misfortunes of his enemies.

Reg is a robot who appears to be a little boy. His actual age, origins, and even name are unknown, as he can't recall anything about his life before his encounter with Riko in the First Layer of the Abyss. Riko named him Reg after a dog she used to have. Reg's body is extremely durable and resistant to physical damage, and is much lighter than its size would suggest. His arms can be extended to be 40 meters in length, and each of them has a built-in Incinerator relic. These high-powered beam cannons are capable of reducing to ashes almost anything; however, his Incinerator is a weapon of last resort as even a single shot depletes the body's energy almost completely, which in turn makes Reg lose consciousness for 2 hours ten minutes after its use. Having an artificial body, Reg may be the one of the only intelligent beings completely immune to the Curse of the Abyss. Because of this, he is sometimes referred to as an "Aubade" or the "Treasure of the Deep". Despite being a formidable fighter, Reg is rather shy and unassertive. He blushes easily and often cries when in distress. Unlike Riko, Reg becomes easily flustered when in danger, and must often rely on Riko's judgment in difficult situations. (Source: Wikipedia, edited)