Umi no Shiro, Yama no Jou

is a Japanese light novel series written by Kaori Aino. The series began publication on December 10, 1995 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
The rich land "Milkwaji Peninsula" where spirits live. The land was ruled by a royal family with the cognitive ability of spirits. One day, a twin prince of Olin and Leon was born in the thunder and roar at the "Castle of the Sea" at the southern tip of the peninsula. The two princes, born under the watchful eye of the god of water and the sun, were born with a unique ability to recognize spirits. Taking advantage of his royal status, King Ashdoto in the "Castle of the Middle", who continues to fertilize his own stomach, had a nightmare with thunder on the day of their birth. Fearing the power of the prince born in the "Castle of the Sea," Ashdoto plans to keep the prince at hand.