Tatsu-Ou (達王, King Tatsu) was the great king who once governed the kingdom of Kei. Kei prospered for three hundred years under his rule and Enho had been one of his closest advisors. Though he inflicted great hardship upon his people at the end of his reign, he is remembered for governing wisely and peacefully throughout the majority of his rule. Tatsu is also the ruler who created the Suiguutou, one of the royal treasures of Kei.
After his death, he was succeeded by a series of female rulers. The successive three proved to be ineffective rulers with extremely short reigns and very long inter-regnums. As a result, the expression "Kaitatsu (懐達)" came into being; the term literally means "to miss Tatsu" or "to pine for Tatsu" and expresses the increasing disappointment the people in the kingdom of Kei has for female rulers. Consequently, the fourth succeeding female ruler to come after Tatsu, Youko Nakajima, struggles against tremendous odds to assert herself in her court.