was a Major and 4th Thaumaturgist Squadron Commander of the Novus Orbis Librarium
When Jin was a little boy, he was very dependent on his older brother, Ragna, for affection and constantly pestered him to play with him. He saw his sister Saya as an obstacle of getting his brother's attention and constantly bullied her in retaliation. Eventually, Ragna decided to look after the sickly Saya and distanced himself from Jin, thus increasing his jealousy.
It was then Yūki Terumi
entered Jin's life and told him about the Black Beast
, that it would be born from Ragna
, and that he is destined to destroy it. Deciding that his brother must pay for his ignorance, and to get rid of the obstacle between them, Saya
, Jin left Terumi
to do as he pleased, including burning the church where they stayed and murdering their caretaker
. When Ragna
arrived, he only watched in shock as Terumi
cut off his arm, and kidnapped Saya
. Jin later vanished from Ragna
's life, and apparently his memory of that incident was blocked off.