While it retains the general architectural style of Edo period fortifications, the castle bears some resemblance to a real castle in Central Japan named Katsuyama, located in Katsuyama , in the Fukui Prefecture.
The real Katsuyama Castle is a less known tourist attraction in Japan which is a late 20th century reconstruction of the original castle founded by Shibata Katsuyasu in 1579.
It is notable that just like the real Katsuyama, the in-game castle also has 6 floors. The real castle also houses museums (one on every floor). The in-game castle features a museum in its basement. There is also a possible in-game reference to the real Katsuyama on the 2nd floor, in the dojo, which features a samurai armor and a traditional samurai table with a katana on display. On the 3rd floor of the real Katsuyama Castle there is a museum featuring various samurai artifacts.
Like most Japanese castles, Katsuyama Castle was a fortresses constructed primarily of wood and stone. Typically these castles evolved from the wooden stockades of earlier centuries, and came into their best-known form in the 16th century. Castles in Japan were built to guard important or strategic sites, such as ports, river crossings, or crossroads, and almost always incorporated the landscape into their defense.
The Yamaguchi-gumi has its headquarters in Katsuyama Castle, located in an unknown isolated mountainous region of Japan, from where Masahiro Hayamoto Sr. carried out operations all across Japan as well as overseas operations in Asia and the United States.