Premise: Hayashi castle was a 15th-century castle, (alternatively known as Hayashi-jo, Fukuyama-jo) in Satoyamabe village, Matsumoto city, Nagano, Japan. A mountain-type castle, it is now largely in ruins. The site is sometimes regarded as one castle, or two castles, Hayashikojo (the small castle) and Hayashiohjo (the larger castle).
Hypothesis: The castle Hayashi (Hayashi-jo, Fukuyama-jo, or Hayashikojo and Hayashiohjo) is considered to be in the Satoyamabe village but also in Matsumoto city, located in the Nagano region of the island nation.