Once belonged to Makara Naotaka's son, Makara Takamoto.
Another theory said that he was used by Naosumi, Naotaka's younger brother instead.
Jiroutachi is supposedly not his real name, as there was a custom to name two swords that belonged to the same person by Tarou for the longer one and Jirou for the shorter one (like Sword No. 1 and Sword No.2). Following the naming method in the game, if he were to introduce his real name it should be 'Chiyotsuru Kuniyasu' or simply 'Chiyotsuru'.
During the Battle of Anegawa fought between Oda Nobunaga - Tokugawa Ieyasu allied force and Asai Nagamasa - Asakura Yoshikage, the Makara father and son fought while wielding Taroutachi and Jiroutachi. However, as the battle went on, they grew weary and Sagisaka Brothers, the three warrior brothers working for Tokugawa's side, managed to defeat Naotaka. Takamoto lost his willpower to fight when he learned of his father's death and was defeated as well.
As they were forged by different smiths, it's presumable that he refers to Taroutachi as an elder brother much like how a junior would treat his senior at an organization.
In many fanworks, Jiroutachi is often seen drinking with fellow drunkard Nihongou.