|Nickname:||Hero of Ikaruga|
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.
Jin was later adopted to the high-esteemed Kisaragi family. With his talents, he rose up in the ranks of the Novus Orbis Librarium and was given by Imperator Librarius the Nox Nyctores named Mucro Algesco: Yukianesa, but his other siblings never trusted him, thinking that he only got his ranks due to his adoption. Indeed, Jin himself felt completely empty even after being showered with awards and ranks (which included the stopping of the Ikaruga Civil War).
When the rumors of the "Grim Reaper" arose, Jin felt a sudden urge to meet him, which caused him to abandon his post and head to Kagutsuchi to find out about the Reaper. When it turns out to be Ragna, Jin became ecstatic to meet his beloved brother and his psychosis caused him to be eager to kill him and fulfill his destiny.
During one of the time-loops, Ragna and Jin's battle is interrupted by Nu's appearance and she ends up throwing herself along with Ragna into the Cauldron. Never wanting to lose his brother again, Jin jumps into the Cauldron despite his wounds and is sent back in time to the year AD 2099/12/31, where he meets Rachel Alucard and is offered a chance to be a true hero. From this point on, Jin becomes one of the Six Heroes, Hakumen.
During the True Ending, Jin is incapacitated badly by Ragna and is sent to the hospital. When he awakes, he finds that he is being targeted by NOL for assassination, thus runs away from the hospital and goes into hiding while cutting off all ties with the Kisaragi family. However, he also hears about Ragna and his subordinate Noel Vermillion staying together, and as Noel reminds him very much of Saya, Jin decides to attempt to kill them out of jealousy. Over time, his willpower becomes strong enough to resist Yukianesa's influence, thanks to the help of Jubei. Jin assisted Hakumen to defeat Mu, but neither had any success. He, Ragna and Noel found that Hazama is working for their sister Saya and Tsubaki sided with them, which is a shock to him. After they left, he, Ragna and Noel decide to become stronger and finding what the true motive is. Jin is currently training under Jubei, possibly to better control Yukianesa.
In the Wheel of Fortune Drama CD, which shows the timeline where Noel did not exist, it is revealed that when they were young, Jin and Saya were very affectionate towards each other. They were happily playing together, and Jin's attitude towards Saya is completely different from the current timeline, with Saya giving Jin a crown of flowers she had made, and saying that she loves Jin very much. This is seen through a vision by Tsubaki, and she immediately displayed jealousy towards Saya, screaming at her to get away from Jin.
Jin's hatred for Saya in all other timelines is likely caused by the Power of Order, which acts as an antithesis to beings such as Observers and Murakumo Units. The Power of Order requires absolute will, which just so happens to be present within Jin (and Hakumen by extension). Whereas Observers have the ability to alter or create phenomena, those with the Power of Order can reject and destroy phenomena. Noel Vermillion is one of the few people who can nullify the Power of Order.