There was a regulation in terms of Imperial succession in those days such as the succession between brothers, the succession of eldest brothers, being nominated by aides, following the will of a former Emperor, etc, (there was a theory developed from a recent study that there was an age limit, up to thirty years old, for succeeding to the throne), it is presumed after fulfilling such complicated requirements, Imperial succession was decided.
この頃の皇位継承のルールには、兄弟承継、大兄承継、群臣推挙、先帝遺詔（更に近年では即位要件に年齢制限（30歳以上）があったとする説もある）などがあり、これらが複雑にからんで皇位継承が行われていたと推定されている。