Imperial Prince Tsuneyo (恒世親王)
Imperial Prince Tsuneyo (805 - June 13, 826) was a member of the Imperial Family during the early Heian period. He was the first Prince of Emperor Junna and his mother was the prince of Emperor Kanmu, Imperial Princess Koshi (who was the titled Empress after her death and a half sister of Emperor Junna). He had a son, Prince Masamichi and a daughter who would become FUJIWARA no Mamoru's lawful wife.
The position of Imperial Prince Tsuneyo (called 'Prince Tsuneyo' in those days) had been complicated since he was born. His father Imperial Prince Otomo (who would later become Emperor Junna) was the son of Emperor Kanmu and his wife FUJIWARA no Tabiko, meaning that he was not a son by an empress like Emperor Heizei and Emperor Saga, who were the sons of the Empress (FUJIWARA no Otomuro), and thus strayed from the heir to the imperial throne according to Emperor Kanmu's policy. However, the Ceremonial House of the Fujiwara clan, or the maternal relative of Otomuro, was stagnating during this period. It is therefore assumed that, in order to strengthen the political position of the Imperial Princes of the Empress, Imperial Princess Koshi, who was the maternal sister of Heizei and Saga, was made to marry Imperial Prince Otomo, who had a mother from the same the Ceremonial House of the Fujiwara clan. However, the situation became complicated because Imperial Princess Koshi gave birth to Tsuneyo before the Empresses (Imperial Princess Asahara and Imperial Princess Takatsu, respectively, on this occasion) of Emperor Heizei and Emperor Saga. This meant that the Imperial Family closest to the direct descendant of Emperor Kanmu, next to Emperor Heizei and Emperor Saga, was Tsuneyo. On this occasion, Emperor Heizei already had Imperial Prince Takaoka, and Emperor Saga later had Emperor Ninmyo. However, Takaoka's mother was from the Ise clan and Masara's mother was from the Tachibana clan, which meant that Tsuneyo was closer to Emperor Kanmu when compared with Takaoka and Masara. Accordingly, Prince Tsuneyo came to be considered as the heir to imperial throne next to Heizei and Saga. Moreover, as there had been no practice where a child would become emperor ahead of his father while the father was alive, it was required to approve Imperial Prince Otomo as the heir to the imperial throne in order to have Tsuneyo ascend the throne. Imperial Prince Otomo became concerned about the circumstances and offered demotion from nobility to subject, attempting to withdraw from being the heir to the imperial throne for himself and Tsuneyo. However, Emperor Heizei and Emperor Saga did not accept this, and when Imperial Prince Takaoka, who was the crown prince of Emperor Saga, died in the Kusuko Incident, Imperial Prince Otomo became the Crown Prince on the premise that Tsuneyo would succeed to the imperial throne.
Imperial Prince Otomo was enthroned on June 2, 823 and became Emperor Junna. With the Retired Emperor Saga's strong desire, Prince Tsuneyo, who was Jushiinoge jiju (Junior Forth Rank, Lower Grade Chamberlain) on this occasion, was installed as the Crown Prince on June 4, 823. However, Prince Tsuneyo excused himself from being the crown prince on the same day, and Imperial Prince Masara (Emperor Ninmyo), the son of the Retired Emperor Saga, was installed as the Crown Prince. Although no reliable record has been found, "Nihonkoki" (Later Chronicle of Japan) suggested that Prince Tsuneyo was given the title of Imperial Prince on this occasion and awarded the rank of Sanbon (the third rank of the Imperial Princess's ranks). He was appointed as jibukyo (Minister of the Ministry of Civil Administration) on November 8, 823, and Nakatsukasa-kyo (Minister of the Ministry of Central Affairs) on December 1, 823. However, Prince Tsuneyo died of disease at the age of just 22 with his title of Nakatsukasa-kyo in 826. Emperor Junna was so disappointed with his son's death that he could not attend to the government affairs, thereafter he got custody of Prince Masamichi and adopted him (who would later be adopted by Emperor Ninmyo).