Emperor Tenmu discontinued the Imperial succession between brothers to stop disputes due to the Imperial succession after his era, it was said he tried to set up a rule for the male in his direct line to succeed the throne, he allowed Prince Kusakabe become Crown Prince.
天武は、自身以降の皇位承継紛争を防止するため、兄弟承継を廃止し、直系男子が皇位承継するルールを定めようと試みたらしく、草壁皇子を皇太子に立てた。