As for the imperial line before that period, Nakatsusumeramikoto ron; if the existence of Empress or Princess who was a liaison between God and Emperor advocated by Nobuo ORIGUCHI, is considered, female-line Emperors might have existed (some people say that they were neither female-line nor male-line but female & male-line Emperors).
それ以前の皇統については、折口信夫の主張する中天皇論等を考慮すれば、女系天皇（純然たる女系あるいは男系でなく双系という意見もある）であった可能性も少なくないとの説もある。