Apparently an easygoing, reckless and somehow comical high-school student known only due to his incapability to arrive on time for classes, he is in fact the result of an experiment made years before by a powerful crime syndicate lord.

The man, dying of old age, tried to use medical knowledge and advanced technology to revive himself as a youth, and thus create a cloning facility where he experimented with cloning humans and transferring memories and experience from a mind to another, so as to be reborn as an ultimate being. His plans failed however, as he died before his project could be brought into fruition, and thus the numerous Shou clones where all scattered far and wide in Japan, each of them focusing on a single area of expertise (be it stunt-driving, surgery, military training, and so on), until two of them encountered each other by chance, thus prompting all clones to reunite and, thanks to the shared experience of them all, vow to redeem Japan and destroy what they perceived as evil, in a similar way of a terror group. 

While their methods are indeed brutal and extremely shocking, one thing has to be noted: the Shou clones all follow something of a code of conduct named one man, one kill, meaning only the chosen target will be put to death, no matter how many clones would be sacrificed in the process (one such example was the assassination of Takeo Tsuruta, where for taking his life 80 clones died). Obstacles such as police or bodyguards are simply evaded or subdued without deadly force.

Also, all the Shou clones are aided in their acts by a peculiar, demonic mask which not only conceals their identity, but also serves as an advanced technological equipment. The mask when donned drills itself into the wearer's skull and links to the brain, so as to assimilate all memories of that Shou and pass it on the others when he dies, normally after a killing. Also, to further prevent the world to understand who they really are, each mask injects a bomb into the head of a Shou on the brink of death, so as to blow his skull and thus prevent recognition, leaving only a headless body behind.

Presenting themselves as terrorists, though making heavy use of costumes and even a cartoonish mascot nicknamed Aametsu-kun, the Akumetsu group (the Shou clones) aim at one thing only: to purge Japan of all whom they perceive as "evil-doers", that is, all those in a position of power who are corrupt and revel in such chaos as a mean to make easy money, or simply those who, while capable of making changes, refuse to do so and only complain. Their executions are always presented as some sort of a show, where usually the Akumetsu, dressed appropriately (from a race driver to a ghost to a businessman) interrogates, frames for their wrongdoings and in the end massacres its intended victims, often in much brutal fashion to which follows his even more grisly death.

Without sermons or pleads, the Akumetsu are also very specific in explaining their motives and objectives to society, and while labeled terrorists by the media and the people, they also gained support from the masses in their bloody quest of disposing of the "evil-doers". To most of them, Akumetsu became not only the name of the "masked men", but also a moniker for the killing of those to be blamed for the crisis.

The anti-heroic protagonist of the series and a third mahai angyo onshi 
from the fallen kingdom of Jushin. Despite the common perception held by Jushin's former 
citizens that angyo onshi are virtuous and bearers of justice, Munsu usually comes across 
as somewhat amoral and does not believe in helping people who refuse to help themselves. 
When he does help others, his methods almost always involve excessive bloodshed, lying, 
torture, and other questionable acts.

Rai is a very elegant, and mysterious Noble. He has no knowledge whatsoever 
of the 21st century, and will often become lost and confused especially with regards to modern 
day technology (such as using a cell phone). He is often used as the manhwa's comic relief with
his love of ramen and the errors he makes with technology. He has fallen into a deep slumber for 
820 years, and had woken up in an abandoned building in South Korea. After seeing what most of 
the humans on the streets were wearing, Rai took on the uniform of a student from Ye Ran High 
School, which is under the administration of Frankenstein, and inadvertently followed the students 
there.

Sagittarius Sisyphus (射手座のシジフォス Sajitariasu no Shijifosu?) is the person who 
took Sasha to the Sanctuary and had laid his a great hope on her. During his known missions, 
he looked for information about Hypnos and Thanatos, finding about the four Dream Gods.

During the invasion of Hades to the Sanctuary, he attacks Hades with a Gold Arrow but Hades 
reverts it easily to his heart and he ends up in a comatose state. His Cosmo is then sealed by 
Hypnos and Thanatos, and his soul is trapped in the Dream World by the Dream Gods. He later 
appears in the final dream of Taurus Aldebaran, reminding him how much it hurts Athena when 
one of her Saints dies.

Sisyphus is no longer in a comatose state, having been rescued by Sasha during the fight 
between Oneiros and El Cid/Tenma. This enables him to assist his fellow Saints against the 
dream god, shooting his golden arrow from the Pope's temple in the Sanctuary, which is 
intercepted in midair and cut in four by El Cid, and then pierces the four weakspots of Oneiros, 
thus rendering him all but vulnerable.

He is entrusted by Hakurei to lead the forces of Athena during the absence of the Pope.

On a side note, when Sasha rescues him inside the dream world, Sysiphus appears briefly 
as a Spectre, clothed with a dark version of his Gold Cloth and shedding tears of blood. To 
date this is the first time since the Hades arc of the original manga that a Gold Saint 
(different from those depicted by Kurumada) becomes a Spectre.

He later appear in Jamir, to lead Athena's army into the Lost Canvas, by using the boat of 
hope. To defend the boat from the attack of Aiacos, Sisyphus uses arrows made of cosmo, 
shooting them with his bow and his direct attack Cheiron's Light Impulse 
(ケイロンズライトインパルス Keironzu Raito Inparusu?) a powerful blast of ray of light, that 
provokes a massive whirlwind, extinguishing all the fire that covered Aiacos' and Athena's ship. 
He was able to reach the eighth sense after blinding himself. Because of the massive cosmos 
he reached Sisyphus could defeat Garuda Aiacos.