Lit.: "Dragon-King Mountain Castle"; a castle built on Mount Ryuuou behind Chougaku Temple by Toichi Tootada around 1533. It was one of the largest castles in Yamato, divided into a North Castle and a South Castle (the North Castle alone was second only in size to Shigisan Castle). Tootada died in 1545, and his son and heir Toichi Tookatsu became master of the castle. When Miyoshi Nagayoshi took power in the capital, his vassal Matsunaga Hisahide invaded Yamato. Tookatsu formed an alliance with Tsutsui Junkei to fight him, but his daughter was taken prisoner, and Tookatsu submitted to Hisahide.

In 1564 at Miyoshi Nagayoshi's death, Tsutsui Junkei formed an alliance with the "Miyoshi Triumvirate" against Matsunaga Hisahide. Toichi Tookatsu was unable to defend Ryuuouzan Castle against the Akiyama Clan, who were allied with Matsunaga. He abandoned Ryuuouzan Castle, and the Akiyama Clan set fire to the castle and countryside. This led to the legend of the 'hoihoi fires' (also known as the 'janjan fires'), which says that on a summer evening when it looks like rain, firefalls will come flying at the person who shouts 'hoihoi' towards the castle ruins.