Tatsuya Shiba is revealed to be a top-tier Strategic-Class Magician operating under the military codename Ooguro Ryuuya in the JSDF's 101 Independent Magic-Equipped Battalion. As a child, his mother Miya and aunt Maya subjected him to radical artificial magic-calculation surgery. This procedure stripped him of natural emotional feelings—except his instinctual drive to protect Miyuki—while providing him with two supreme abilities: Decomposition (reducing matter and magical formulas to atomic components) and Regrowth (reverting physical injuries within 24 hours while absorbing all cumulative pain in an instant).
In Season 1, Tatsuya single-handedly obliterates an invading fleet from hundreds of kilometers away using Material Burst, converting mass directly into nuclear-scale energy. Season 2 unveils extra-dimensional Parasite entities infiltrating human mages, leading to an alliance with USNA operative Lina. Season 3 resolves Zhou Gongjin's Kyoto conspiracy and exposes artificial human engineering programs involving Minoru Kudou. The season ends with Maya summoning the siblings to the Yotsuba estate, setting up the Yotsuba Succession Arc where Miyuki is declared clan successor and betrothed to Tatsuya to officially secure his position.