Where his brother Ragna is hot-tempered and quick to draw first blood, Jin is cold, aloof, and borderline sociopathic. He cares little for the feelings of others, and denounces, in his own words, trivialities like camaraderie, believing that such things are lies that people use to their advantage. He has no compunction with killing anyone who gets in the way of his goal. In addition, he repeatedly shows that he dislikes reminiscing about the past, particularly about his days at the Military Academy.

This, however, is all a façade. The moment he reunites with Ragna, Jin loses his calm, detached demeanor and reverts to his childhood self. His voice becomes noticeably more ecstatic, and he is now prone to fits of maniacal laughter, mostly due to Yukianesa's influence (which compels him to kill his brother due to his nature as the Black Beast, as well as the Power of Order, which perceives him as a threat to the stability of the world). In the past, Jin would often cling to Ragna for assistance with everything, which greatly annoyed him and was jealous of Saya when Ragna spent more time with her. However, it is shown during the first time loop that Jin loved his sister Saya as much as he did Ragna.