This is based on the theory that Emperor Kotoku sent a poem to his wife Hashihito no Himemiko (Emperor Tenchi's (Tenji) sister with the same mother) indicating that Emperor Tenchi (Tenji) was having an affair with her, which is contained in "Chronicles of Japan (Nihon Shoki)."
これは、『日本書紀』に記載された孝徳天皇が妻の間人皇女（天智の同母妹）に当てた歌に彼女と天智との不倫関係を示唆するものがあるとするものである。