Kondo Isami was the commander and Chief of the Shinsengumi, and was Nagasone's proper owner. Fellow Shinsengumi swords are Izuminokami Kanesada, Horikawa Kunihiro (owned by Vice-Chief, Hijikata), Kashuu Kiyomitsu, and Yamatonokami Yasusada (owned by Captain Okita). Although his Katana was said to be Kotetsu, it was often thought that Nagasone's real creator was Minamoto no Kiyomaro, whose creations have yet to appear in Touken Ranbu. Kondo led rounin, including the above two members, and under the samurai Matsudaira Katamori they became the Shinsengumi and eventually an official police force.
However, due an assassination carried out on Sakamoto Ryōma, Kondo was executed and the Shinsengumi dissolved. Three years later the Mimawarigumi chiefs would confess to the crime, but Tani Tateki, a higher up official, said that Kondo was not falsely accused.
This fact is why he and Mutsunokami Yoshiyuki have a recollection together, and furthermore why Nagasone is antagonistic towards him in the recollection; Mutsunokami is Sakamoto's sword.
While in the book description he himself admitted that he was made by Minamoto Kiyomaro, there existed a theory that he might be crafted by Kotetsu's adopted son, 2nd generation of Kotetsu, and thus might be the reason his school was listed as 'Kotetsu...?'.
Was only obtainable through Kebishii drops until 2016/03/15. He can be forged since.