The Three Sisters refers to three large islands off the eastern coast of Umbria. The sea between them is incredibly dangerous for two reasons: shallow reefs and sudden storms. Pirates often use this as a means of escaping pursuing Elk vessels, though at great personal risk.
Legend has it that long ago, this area was actually one large island where the Kraken clan ruled. Renowned for their prowess at sea, their king, King Architeuthis, made the claim that their sailors were the true masters of the ocean. Mordrith heard this, and as punishment for their pride sent a huge storm that sunk their entire island.