Tatsuya Shiba's History
Tatsuya is the eldest son of Shiba Tatsurou and Shiba Miya. He is eleven months older than his younger and only sibling Miyuki. His birthday falls on April 24th. They are often mistaken as twins for being in the same school year, though sometimes they are not immediately recognized as siblings in general.
Prior to the beginning of the series, their father remarried six months after their mother's death; with the siblings now living on their own at the Shiba Residence which is described as a place that vastly exceeds the average size.
From a young age, one of the only things for which Tatsuya showed anything resembling enthusiasm was in Magic Engineering and CAD development. He has an aptitude for them and has continually displayed his interest until the present day, as he is aided by the circumstances. Their house has a basement with the same floor layout as the floor above but remodeled as Tatsuya's lab. It is equipped with state-of-the-art equipment from Four Leaves Technology with plenty of space for him to develop and test any new types of Magic that he may require.
NOVEL ONLY SPOILERS
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Tatsuya is a child born of the Yotsuba family. From birth he was the apparent heir for the Yotsuba Family; but after the birth of his sister Miyuki and the discovery of his lack of ability to wield magic as it was intended, he was reduced to being Miyuki's Guardian. Despite the facts of his parentage, he isn't accepted as a legitimate member of the family by many due to the fact that he cannot wield magic freely; the two types of magic he can freely wield are not considered magic by the family's standards due to their nature of only 'destroying' and 'restoring' information, not 'altering' them.
In the present time, aside from his two natural forms of magic, he is only able to use imitation and theoretical magic; something which can be ascribed to his other unique abilities and superior intellect. Despite this deficiency he has taken advantage of his physical prowess and his superpowers to become Miyuki's Guardian, which is considered to be a job of the highest importance in the Yotsuba Family. His combat prowess has also become respected enough that he is now a primary combatant of the Yotsuba Family.
Artificial Magician Experiment
Tatsuya's Magic Calculation Area is dominated by his powerful innate abilities, such as Decomposition, Regrowth, and Elemental Sight. It is due to this imbalance that he is unable to use any other form of magic. So, to enable him to be able to use other magic spells, especially the Systematic-Type Magic, his mother, Shiba Miya, and her younger-twin sister, Yotsuba Maya, performed the Artificial Magician Experiment on the 6-year-old Tatsuya. Miya used her unique and forbidden Outer-Systematic Magic Mental Design Interference, forcibly altering the area in the consciousness that is responsible for strong emotions (called the Limbic System) and installed a Magic Calculation Model in an attempt to create an Artificial Magic Calculation Area.
However, the strain of the operation resulted in Tatsuya losing his ability to feel any type of strong emotions except for those regarding his sister. Even with this exchange for the installation of another Magic Calculation Area which granted him the ability to utilize normal magic (albeit at a significantly lower speed and power) it was still insufficient for him to be regarded as a 'true magician' by the Yotsuba's.
An additional side effect of this procedure was for Tatsuya to develop a perfect memory, allowing him to recall all of his memories with complete accuracy ever since the day of the experiment.
It was later revealed by Maya that the operation was, in fact, to modify Tatsuya so he would not lose control of his emotions and become a berserker, destroying the world with his magic. In order to ensure that Tatsuya had something that he was attached to, Miyuki in this case, Miya removed all his emotions, but for some reason, that was beyond Miya's and Maya's understanding, he kept his love for Miyuki.
Revelation of the past
It is revealed that Tatsuya's powers Regrowth and Decomposition were influenced by the will/prayers of the Yotsuba (particularly Maya and Miya) for a superman-like savior when he was just a fetus.
In the aftermath of the Nightmare of 2062 which resulted in the destruction of Dahan but also caused the death of nearly half of the members of the Yotsuba, they wished for a child that would protect them from any similar fate. When Tatsuya was born, the Yotsuba originally celebrated his birth, but due to the destructive potential of his magic, Kuroba Juuzou proposed the idea of killing the new-born baby, Tatsuya, but the Head of the Yotsuba Clan at the time, Yotsuba Eisaku rejects the idea and decides to take advantage of Tatsuya's power for the Yotsuba.
Since then, despite Tatsuya being a baby, he was raised to be a combat magician under Eisaku's oversight. As early as when he was able to stand up, he was subjected to training in the optimization of his body. Tatsuya soon became able to walk and the combat training began. No matter how hard he cried and screamed, his will was ignored. As the family always resorted to locking him up, Tatsuya soon gave up on his rebellious attitude. Starting from killing a wild animal, then a military-grade dog, then a military strengthened animal, and finally a living soldier. Tatsuya first killed a man when he was six, immediately after the artificial magician experiments. He sank in a skilled 30-year-old combat magician in a pool of his own blood from the very start in combat, neither out of an accident nor a surprise attack.
After Yotsuba Eisaku passed away, Maya took over the position of Family Head and continues Tatsuya's training. Then, Maya and Miya performed the Artificial Magician Experiment on Tatsuya. Later Tatsuya was assigned as Miyuki's Guardian.
Revelation to the world
Maya announces that Tatsuya is her son and also Tatsuya and Miyuki's engagement, Tatsuya is freed from the position of Miyuki's Guardian. He is then formally recognized as a Yotsuba
