He is first introduced as an amnesiac and a former battle sklave who was captured by the Barsburg Empire and was considered to be the military academy's star pupil. It is later revealed that Teito is the son of the late king of Raggs, Weldeschtein Krom Raggs, who was killed when he was a child, thus making him the prince of the Raggs kingdom, his homeland. His mother is Weldeschtein's beloved concubine or unofficial wife, Millea Klein. Through political marriage to King Weldeschtein, Princess Vanessa Antwort is Teito's stepmother and King Antwort is his step-grandfather.
After the Raggs War, Teito is one of the only three surviving members of the Raggs royalty, with the other two being Millea and Ayanami, who has been revealed to be his paternal uncle.
Teito had been entrusted with the Eye of Mikhail, a powerful Eye which holds the God Mikhail, since his childhood to protect him against the death God Verloren, whose body he contains as Pandora's Box. After Teito escaped to the Barsburg Church in order to avoid a treason charge, he has made it his goal to destroy Verloren's body.
Along with Frau and the Fyulong reincarnation of his best friend, Mikage, Teito travelled across the seven Districts to search for the Cursed Tickets to go to the land of Seele, thus attempting to fulfill the task Fea Kreuz and the previous generation of Seven Ghosts were unable to complete: to execute Verloren. However, in the wake of Ayanami's sudden death, Teito instead goes to Seele to save Frau from Verloren's scythe, and returns to the human world as a baby. Forty years after his reincarnation, he reestablishes his kingdom. [Source: wikia]
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