I have outlined a very brief history of the Mad Shugenja's castle, and uploaded level 1D of the castle here.
For over 200 years, the Mad Shugenja Katsushiro ruled over the western mountain valley and it's people. He conducted strange experiments on the local inhabitants and twisted them for his cruel purposes. They dug out his vast underground crypts and laboratories, and quarried the stone used to build his extensive castle. Many foul and dangerous beasts came to serve under this wicked master, further terrorizing the local populace.
As Katsushiro continued to grow his domain, he came into contact with the western reaches of the Mifune Shogunate. Initially these meetings were small border clashes, however as the Shugenja grew in power he began regular raids and incursions into the Shogunate's realms to gather slaves and fodder for his experiments. These actions caused the local Daimyo to request assistance from the Shogun who sent a large force to deal with the Mad Shugenja.
The armies clashed in the valley below the twin peaks of the Mad Shugenja's Castle. The fighting lasted for 3 days and was so fierce that the creeks that flowed from the mountains ran red with blood. (These mountains are now called Blood mountain and Slaughter mountain). In the end, the Shogun's forces prevailed with the aid of the hero Ito Matsumura and his holy sword “Burning Mist”. He led the last charge of the forces against the Mad Shugenja himself deep in the pits of the castle. He was killed as he struck the final blow against Katsushiro, and his body was lost in the route of the evil forces, never to be recovered.
The son of Matsumura, then 13 year old Juro was given permission to build a castle in the mountain valley in recognition of his father's feats. In time Juro became the leader of the Goma Castle town and the village that grew up around it. He is a man of peace and the peasants love him for it. He is now 86 years old and still runs the castle.
Lately there have been sightings of evil creatures in the mountain forests at night, and the only son of Juro Matsumura (Menzo aged 41) has gone missing. There are rumors that the bones of Katsushiro are restless and he is calling a new army to serve him.