Spike Spiegel is a tall and lean 27-year-old bounty hunter born on Mars. The inspiration for Spike is found in martial artist Bruce Lee who uses the martial arts style of Jeet Kune Do as depicted in Session 8, "Waltz For Venus". He has fluffy, dark green hair (which is inspired by Yusaku Matsuda's) and reddish brown eyes, one of which is artificial and lighter than the other. He is usually dressed in a blue leisure suit, with a yellow shirt and Lupin III inspired boots. A flashback in Session 6 revealed it was his fully functioning right eye which was surgically replaced by the cybernetic one (although Spike himself may not have conscious recollection of the procedure since he claims to have lost his natural eye in an "accident"). One theory is that his natural eye may have been lost during the pre-series massacre in which he supposedly "died". The purpose of this cybernetic eye is never explicitly stated, though it apparently gives him exceptional hand-eye coordination - particularly with firearms (Spike's gun of choice is a Jericho 941, as seen throughout the series). In the first episode, when facing a bounty-head using Red Eye, Spike mocks him, calling his moves "too slow". At first, this seems like posturing on Spike's part, but even with his senses and reflexes accelerated to superhuman levels by the drug, the bounty cannot even touch Spike. A recurring device throughout the entire show is a closeup on Spike's fully-natural left eye before dissolving to a flashback of his life as part of the syndicate. As said by Spike himself in the last episode, his right eye "only sees the present" and his left eye "only sees the past." Spike often has a bent cigarette between his lips, sometimes despite rain or "No Smoking" signs.

Oga is easily agitated and is always willing to fight, unless it will bring out the Zebub spell. He appears to have his own skewed idea of what a 'man' should be like, and attempts to pass on these ideals to Be'el. Despite being called evil by almost every character of the series, he has shown to have a calmer and, if only slighlty, warmer side to him, shown when he speaks with Hilda about his position as Be'el parent and assuring Lamia that if Be'el ever got sick again he would call her immediately.

Yagami Light is a brilliant college student. Nicknamed as "Kira", he uses the death note to create his ideal world of justice under him; its new god. Though he looks frail, Light is an extremely athletic person, with an aptitude to find an opponent's weak point. He is a genius, which adds to his notion that only he is fit to judge humanity and steer it on a proper moral course.

A small-time criminal who was in a gang with his best friend, Harry McDowell, along with three other close friends. After these three were killed, Brandon and Harry joined Millennion, a powerful mafia-type organization formed by Big Daddy. Brandon was trained by the Millennion's Bear Walken to be a sweeper (hitman), eventually forming his own elite sweeper unit within Millennion called True Grave. Even as Harry rose to power, Brandon remained loyal to Big Daddy for Maria's sake.

Orochimaru (大蛇丸?) is one of the primary antagonists of the Naruto series. In the series, Orochimaru is a former ninja of Konohagakure and a student of the Third Hokage. During his time in the village, he distinguished himself as one of the village's most powerful ninja along with his teammates, Jiraiya and Tsunade. His desire to obtain immortality led him to conduct experiments on other Konohagakure ninja, and he eventually fled the village and joined the criminal organization Akatsuki. After attacking fellow Akatsuki member Itachi Uchiha, who defeats him, he leaves Akatsuki and establishes his own ninja village, Otogakure, in the hopes of destroying his former home. His immortality technique involves transferring his consciousness between different host bodies, and his desire for a new host, particularly Sasuke Uchiha, is one of his driving motivations throughout the series.