Although imperial succession by direct descendants was ideal, a male successor to the throne was not always assured, and at all times there was the risk that the line of succession could be severed.
直系相続による皇位継承は理想的である反面、皇位継承男子が必ずしも確保できる訳ではなく、常に皇統断絶の不安がつきまとう。