|Spoiler Alert: This page contains spoilers. Read at your own risk.|
Ooguro Ryuuya (大黒 竜也) is an unregistered Strategic-Class Magician of Japan, and a Special Officer of the 101 Independent Magic-Equipped Battalion led by Major Kazama. The real identity of Ooguro Ryuuya is known only to a few select people that are connected to him and his affiliates.
He is called the 'Obsidian Demon' because he appears in battlefield wearing a pure black mobile suit, the uniform of the battalion.
- Main Article: Shiba Tatsuya
Oogura Ryuuya is Tatsuya's alias in the military.
Tatsuya fought with the army at the age of 13, when he sought vengeance for his sister against the invading forces in Okinawa. For the cost of shooting his sister, he applied the theory of Mass-to-Energy (aka Matter-to-Energy) conversion that had not been verified experimentally before, and obliterated the enemy that was trying to invade Okinawa. That was the first time he used the Strategic-Class Magic that converts matter into energy, which had only existed in theory.
He serves in a special military unit called the "101 Independent Magic-Equipped Battalion" under Major Kazama Harunobu.
After Tatsuya was announced to be a member of the Yotsuba Family, the only reason left to keep his existence as "Special Officer Ooguro Ryuuya" a secret was because of the confidentiality of him being a Strategic-Class Magician. 
He destroyed the invading ship moored at Yokohama port while it was trying to escape using the weaponized CAD "Third Eye," casting the Strategic Class Magic "Material Burst" for the first time. He destroyed the ship some ways off the coast because the contents within the ship could bring harm to the aquatic life in the sea if they spilled.
Ooguro Ryuuya is also the cause of the Great Asian Union's fall during Scorched Halloween when he obliterated the entire enemy fleet at the Zhènhai Naval Port and killed the Great Asian Union's Strategic-Class Magician in the process.
Volume 13 reveals that the JSDF knows about the epithet (Mahesvara) given by the Great Asian Union soldiers.
In AD 2092, an unidentified 'demon' smashed the Great Asian Union in Okinawa. Comments/Reports about him from the soldiers, who returned through prisoner exchange, occurred in English in order to get around the gag order issued by the upper echelons of their military, who officially denied his existence.
Ooguro Ryuuya is referred to as "Mahesvara" . It also refers to his ability to heal (using Regrowth) his allies and annihilate the enemy from existence (using Mist Dispersal their bodies are completely destroyed) which are also the powers of the "Mahesvara". This is something the soldiers of the Great Asian Union are forbidden from mentioning since it is a nightmare best left untouched. He is mentioned to excel at extreme long distance precision attacks and over the horizon sniping, which other Strategic Magicians and regular Magicians seem to be incapable of. In part to his immeasurable strength, power, and intellect he is called "God of Destruction" (another name for Mahesvara) by Raymond Clark.
|“||He was someone who wielded incredibly destructive power on the scale of nuclear weapons and may very well one day shatter the world.||”|
—Tatsuya contemplating to himself, Volume 12, Chapter 2
- Main Article: Decomposition
Demon Right is what the Great Asian Union soldiers called Tatsuya's Mist Dispersal Magic that destroyed the Great Asian Union soldiers in 2092, and once again three years later. It activates every time he raises the CAD in his right hand, and the targets dissipates like mist in the air.
Anything that the right hand points at, fades away into dust after burning, hence the unofficial title given to the technique.
- Main Article: Regrowth
Divine Left is what the Great Asian Union soldiers called Tatsuya's Regrowth (Restoration) Magic, and is the complete opposite of Demon Right, in that it activates through the CAD held in his left hand. It does not inflict any damage, but reverts the soldiers on the brink of death, back to their former selves before the mortal injuries.
Fallen soldiers with fatal wounds recover, without even holes in their armor.
- "Ooguro Ryuuya" can be roughly translated into "Great Black Dragon". This is keeping with Shiba Tatsuya's heavy dragon symbolism. The name is also a reflection of Daikokuten (大黒天), the Japanese variation of Shiva, and the god of darkness and blackness. The characters for Ryuuya (竜也) can also be read as Tatsuya. Coincidentally, Mahesvara is also an alternate name of Shiva, who in Japanese is commonly pronounced as Shiba.