Hero's Grave
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The Hero's Grave is a large castle that appears in the Middle Ages and the Present. Prior to Frog visiting Cyrus's gravestone there and powering up the Masamune, it is known as the Northern Ruins. To fully explore the ruins and power up the Masamune, the party must hire the carpenter in 600 A.D. In order to hire him, you must aquire the Carpenter's Tools in 1000 AD. Then, clear out the Ruins of monsters. Hire the carpenter for a small fee, and after that Cyrus's grave is accessable.