Hajime Saitou is loosely based on the real third-squad captain of the Shinsengumi. During the Meiji era, he lived as a police officer under the name of Gorou Fujita. In the Rurouni Kenshin series, he plays the role of Kenshin's old rival and enemy from the Bakumatsu. He has no compassion or mercy for his enemies and he lives by the Shinsengumi code "Aku Soku Zan (悪即斬)," literally "Slay Evil Immediately," but more poetically rendered as "Swift Death To Evil." His signature technique is the Gatotsu, a left-handed thrust and a variation of the Hirazuki technique developed by Toshizou Hijikata, the Vice Commander of the Shinsengumi. Although the Gatotsu is a fictional technique only found within the Rurouni Kenshin series, the Hirazuki is a real technique that was used by many of the Shinsengumi members.

The full transformation is very physically different in appearance, and far more powerful than the previous one. In this form, Ichigo has long straight hair, reaching down to his waist, and a Hollow hole, smaller than his previous one. He has retractable claws on his fingertips and toes, small furry red tufts, two starting from his collarbone and stretching around his neck and one each on his wrists and ankles, as well as white skin. In this new form, he has a different Hollow mask. It covers Ichigo's entire head, and its markings are different.The mask features two long forward-pointing horns, with black strips extending from their center towards the tips.
In this form, Hollow Ichigo can destroy a large portion of Las Noches's roof with the wake of a single slash of his sword.He easily tore off Ulquiorra's left arm without much resistance from the Arrancar's Hierro.He crushed Ulquiorra's strongest attack, Lanza del Relámpago, and forced it to collapse before Ulquiorra even got a chance to throw it.He easily slashed Ulquiorra from his left shoulder to his lower right hip through his Hierro.He can effortlessly throw a large portion of rock with a single hand.His crimson Cero has become exceedingly more powerful, capable of completely overwhelming Ulquiorra's Cero Oscuras and causing large scale destruction to large portion of the surroundings. It is fired from between the tips of his horns instead of his fingers as it was during Ichigo's Visored training. However, if one of the horns are cut off, he is unable to form the Cero properly, and any energy already gathered will implode.

The leader of Akatsuki is a mysterious figure. None of the other Akatsuki members refer to him by name, instead simply calling him "leader," and his face is rarely shown. He has the respect of most of his subordinates (Hidan is an exception) and is the one directing their actions. He is also the one to initiate and supervise the jutsu that forcibly brings a tailed beast out of its host. He can also use the Shape shifting Technique (象転の術, Shōten no Jutsu?) to clone his subordinates using human sacrifices, allowing them to engage the enemy without risking themselves. The clones formed are a perfect copy of the target, even possessing the kekkei genkai and unique weapons of the original. Their abilities are proportionate to the amount of chakra given to the clone (in its debut, the leader requested thirty percent). When it becomes necessary to gather his subordinates, he can communicate with them over long distances through some form of telepathy.

The title character of the series, Neuro is a demon detective from hell. He looks for mysteries in the labyrinthine minds of humans for sustenance. When he dismantles the mystery and strips the culprit of all of their defenses, that releases the negative energies that caused the culprit to commit the crime, which he then consumes. He came to the human world in search of the Ultimate Mystery, as all of the mysteries in hell were bland and repetitive. Once in the human world, he forced Yako to be his assistant, and began to solve mysteries.

He is a very self-centered, sadistic and arrogant character that cares little about the human aspect of the cases, most of the time only focusing about getting the mystery as quick possible. This can be a disadvantage, however, as he can't relate to or begin to understand the motives of the culprits. He will also commit blackmail and manipulation to achieve his goals. Neuro enjoys abusing and torturing Yako at every chance he gets, and thinks of her as nothing more than a slave to use at the beginning of their 'partnership'..

Sousuke is an approximately 17 year old sergeant within the paramilitary counter-terrorist force, Mithril. He is a member of the SRT (Special Response Team) of the Western Pacific Battle Group "Tuatha de Danaan". His call sign is Uruz-7 and his ID number is B-3128, and operates as team point-man as an Arm Slave specialist.

In addition to being a capable Arm Slave pilot, Sousuke is a specialist in Arm Slave operations and maintenance, improvised explosives, small arms, survival training, anti-armor combat, trap setting and camouflage. Additionally, he is proficient in logistics, demolitions, breach and forced entry, covert intrusion, and hand to hand combat. His background and experience as a guerrilla fighter, and later a mercenary soldier has made him much more sensitive and knowledgeable about tactics and methods more commonly used by guerrillas than government trained regulars.