Nihai Tower (S6) in the Kakushikoto province was the great watchtower that stood on the only road to Yogo Shiro, guarding a treacherous bit of swamp and cliff walls. From it's vantage point on the edge of Seikitsu sano Yama no Oi its guards could see watchfires in both Yogo Shiro and Shiro no Shosuro. Messages could be passed between the two castles in this manner, and no one outside the Scorpion had ever managed to decipher the code used.