Blue Sea (青海, Seikai) is located east of the Yellow Sea and borders the three kingdoms of En, Kei, and Kou.
- En - The Kingdom of En is a flourishing kingdom of the Twelve Kingdoms that is between Kei and Ryuu and is one of the four "middle" kingdoms. It is ruled by Shoryu who has reigned for 500 years.
- Kei - The Kingdom of Kei is the most eastern kingdom of the Twelve Kingdoms. It is ruled by Youko Nakajima.
- Kou - The Kingdom of Kou is the first kingdom that Youko Nakajima sets foot in and is one of the four "middle" kingdoms. It was formerly ruled by the unnamed King of Kou.