Prince Motoi (Motoi O) (基王)

Prince Motoi (November 20, 727 - October 24, 728) was the first Prince of Emperor Shomu. He was also called Motoi no Miko.
Furthermore, in "Honcho koin jounroku" (the Emperor's family tree, made in the Muromachi period), he was listed only as 'Imperial Prince' with an explanation as 'Imina Prince Motoi.'
Because of that, some say that the explanation was written in error, which should have been 'Prince Motoi (uncertain).'
Since there was no custom of giving the title of Imperial Prince by an imperial order at the time, he should have been automatically given the title of 'Prince Motoi' upon his birth if he was named as 'Motoi.'

He was the only son of Emperor Shomu and Empress Komyo. When the Emperor finally got a son, he felt great joy and installed the son as a Crown Prince only 32 days after his birth. At the time when the adulthood was required for not only an Emperor but also for a Crown Prince, it was an extremely rare move. Prince Motoi, however, became sick the next year and died less than a year after his birth. He was buried on Mt. Naho.

That too early death created a rumor that it was due to the execration by Sadaijin (the minister of the left) Prince Nagaya. Since Prince Nagaya was in a strong position as a successor to the Imperial Throne, the rumor made Emperor Shomu, who deeply mourned over his son's death, distrust Prince Nagaya. And that gradually lead to the Nagayao no Hen (Conspiracy of Nagayao, a political purge caused by a slander).

[Original Japanese]