In Japanese mythology, Futsunushi (経津主神, Futsunushi no kami) is a kami of swords, thus his Shinto priests are supposed to always wear Nihontō with them, at least in the shrine. He is a general for Amaterasu along with Takemikazuchi. He is worshipped at Katori Shrine, and as he is seen as a god of martial arts, Katori Shintō-ryū adepts make a solemn oath when they join the school.
References
Futsunushi Wikipedia(Text) CC BY-SA