Nakigitsune (lit. Crying Fox) is a unique uchigatana (打刀) smithed by one of the members from Awataguchi (粟田口) school, Awataguchi Kuniyoshi (粟田口国吉). Nakigitsune is not associated with any historical figures or wars so it doesn't really have a back story to it. But! It is still a very famous nihontou (日本刀 Japanese sword) because of the details of the nihontou itself.