Empty Void

Empty Void (のヴォイド, Kokū no Voido), who now goes by the alias That Man (あの, Ano Okata; Viz: The Great One), is the founder of the secret Ninja Village.

Appearance
As a human, Empty Void was lean but muscular. He had light coloured long rough hair, which he tied in a ponytail. He wore goggles and a scarf, modern body armor, and a utility belt. He has a more slender build but is around the same height as Blast. His light-colored hair is cut similarly to Blast apart from towards the back where it forms into a long ponytail. He wears multiple pieces of armor on his arms, shoulders, chest, and back. Underneath, he wears all black attire including his gloves and has multiple pieces of cloth wrapped around his torso. His two sheathed katanas are attached to his back and he has what appears to be small pouches held in place on the back of his waist.

As a monster, Empty Void has a monstrous appearance with spiked skin and flamed hair. He has different skin colors on different parts of his body. His teeth are all razor sharp.

Personality
As Blast's partner, Empty Void was probably a good person before becoming a Mysterious Being.

Empty Void is an utterly ruthless, malevolent, cunning, bloodthirsty and despicable individual. Having been alive for more than three hundred years, he has used his powers and skills to assassinate hundreds of thousands of people over his lifetime. He is the founder of the Ninja Village and starter of atrocious regiments children are put through, and even after founding the village, he continued to assassinate people. When killing his targets, if he comes across people with strong bodies, he will take their bodies away to (presumably) use their body parts to stay young and fresh.

He also did not seem to care about the ninjas who banded together for him, as he merely observed Flashy Flash and Speed-o'-Sound Sonic kill all of the members of the Heavenly Ninja Party from a rooftop. He is also very arrogant, as he challenged the top S-Class hero Blast to a fight and was defeated by the hero, being put in a coma for 15 years.

History
In the past, Empty Void, Blast, and a group of other collaborators searched for mysterious cubes that had the power to turn humans into monsters. They figured out that those cubes could allow for communication with "God". They also referred to it as an oopart (out-of-place artifact). At some point after, Empty Void became a Mysterious Being after given powers by "God". After being defeated by the top-ranking hero 15 years ago, he lost consciousness and was put in a recovery capsule.

Empty Void was born about three hundred years ago, although it is unclear whether he was born a mysterious being or gradually became a mysterious being. Since that time, he honed his skills and started his career as an assassin. His unbelievable power and skills allowed him to reach the top of the assassination industry and give him enough ties to rule the world in the shadows. During this time, he killed several high-profile individuals whose names would be passed down in history.

Because of this, Empty Void was regarded as the most powerful ninja to walk the Earth. Sometime in the past, he founded the Ninja Village. The village trained ninja assassins and sent them to factories of the underworld.

Sometime later, Empty Void challenged Blast, but he was defeated and put in a coma. The village placed him in a recovery capsule where he layed dormant for 15 years.

Ninjas Arc
While resting in his hideout, Speed-o'-Sound Sonic is approached by the Heavenly Ninja Party. This party consists of ninjas from previous graduating classes of the village, including Gale Wind and Hellfire Flame. They tell Sonic that Empty Void, who they address as "That Man", has awakened, and reveal to Sonic their plans to kill Flashy Flash and Blast, make Empty Void their leader, and come out of the shadows to take over the world with their superior ninjutsu skills.

After Sonic and Flash kill the entire Heavenly Ninja Party, he is revealed to have been observing the battle go down from a nearby rooftop.

The two later arrive at Sonic's residence, where they find Saitama, sitting over a hole in the ground and holding Empty Void's equipment. Saitama explains that Empty Void approached him and monologued about his legendary demon blades and his immense power. He then attacked Saitama, who easily defeated him with a single downward punch, and was stripped of all of his weapons.

Abilities and Powers
As the leader of the Ninja Village, Empty Void is a very powerful individual.

Supernatural Abilities
Dimensional Travel: Empty Void has the ability to open the "Gate of the Celestial Rock Cave" which connects to the dimension where "God" hides.

While his fighting abilities have not been shown, it is safe to assume that Empty Void is an extremely powerful opponent. Gale Wind claims the Leader has a body count in the 6 figures, and that he is responsible for the deaths of many well-known historic individuals. He stood at the top of the assassin industry and ruled the world from behind the scenes. He is regarded as the most powerful ninja to ever walk the Earth by all the ninjas who graduated from the village, indicating that he possesses S-Class level abilities. This is also shown by the fact that one of his scrolls contains a technique that Flashy Flash used to instantly kill Heavy Smoker, a Dragon-level threat that was shrugging off attacks from Tanktop Master. Gale Wind has described him as possessing overwhelming power, and even after seeing Flashy Flash and Speed-o-Sound Sonic's abilities, he was still confident neither of them would stand a chance. Furthermore, Gale Wind even stated that even if all of the ninjas attacked him together, the leader could handle them as if he were handling an infant.

Physical Abilities
Immense Speed and Reflexes: As the founder of the Ninja Village, Empty Void has amazing speed and reflexes. According to Gale Wind, he can perform humanly impossible ninjutsu moves four to five times in 0.2 seconds, and even if all of the Heavenly Ninja Party members attacked him at once, the leader would be able to handle them all as if he was handling an infant.

Enhanced Longevity: According to Gale Wind, whenever Empty Void found a strong and healthy body, he would take all their blood and innards away from the scene to replace his organs or consume it.

Multiple hearts: Gale Wind states that Empty Void has multiple heartbeats, indicating that he has more than one heart.

Fighting Style
Ninjutsu Master: Being considered the strongest ninja to have ever lived, Empty Void is highly skilled in Ninjutsu. He is evidently proficient in the use of an absurd variety of weapons, and carries them into battle.
 * Sky Ripping Scattered Flash Slash (裂空散閃斬, Rekkū Sansenzan): Empty Void creates powerful hurricanes which he can control by spinning his sword at incredible speeds. Though he's never been seen using it, it can be implied that he can use this technique, since he carried the scroll that detailed how this move is performed.
 * Speed of Sound Electric Discharge Fist: Empty Void extends his finger and pokes his opponents on the head, unleashing powerful shots of electricity and killing them. Though he's never been seen using it, it's also implied that he can use this technique since he carried another scroll that detailed how this move is performed.

Equipment
Swords: Empty Void carries two swords on his back.

Swords: ccording to Saitama, he calls his swords the "Legendary Demon Blades."

Shuriken: Empty Void also carries a variety of shuriken, with many different styles among them.

Kunai: A set of Japanese knives which are common ninja weapons.

Stun Gun: An electroshock weapon for disabling attackers.

Scrolls: Empty Void has several scrolls on him. They appear to contain the details of several forbidden techniques, as Flashy Flash took some of the scrolls left behind by him and learned a new technique.

Baton: A short bludgeon commonly used by police officers.

Pistol: Among the numerous weapons in his collection is a handgun, with two extra magazines.

Taser: A short-ranged variety of electroshock weapon.

Trivia

 * Empty Void's tendency to harvest the bodily remains of felled enemies and graft them to his own flesh parallels the practices of Kakuzu from Masashi Kishimoto's Naruto series. Kakuzu was a super ninja who would harvest the hearts of defeated shinobi and implant them into himself granting him a form of advanced longevity.