The Riddle of Tsukikage Castle

This job, oddly enough, is at Goemon's request. The will of an old man, Kuranari, says that whoever solves the "mystery" and finds his inheritance can have it. Lupin takes the challenge of deciphering the code. But the Fuuma Ninja are also plotting to take the treasure for themselves. The end of the battle over the mystery culminates on the roof of the castle tower. Where is the legendary sword, Tsukikagemaru?!