Juju was a Fu-ma ninja who was possessed by Arahabaki during a mission to check the shrine where he was sealed off. Unable to either stop her or exorcise the demon, Taki had no choice but to kill her. The death of his host angered Arahabaki. He escaped the battle and proceeded to obliterate a nearby village, after which he settled in baby Natsu.
The incident led to Taki feeling guilt for being unable to stop the demon, so she took Natsu as her apperentice to atone for her failure.