Waka poems were a popular art form in the Heian period, enough that the famous poet Fujiwara no Sadaie and Emperor Go-Toba sought to put together a selected collection of chosen verses.
Sadaie's son had married 
Yoritsuna's daughter.
El hijo de Sadaie se había casado
con la hija de Yoritsuna.
O filho de Sadaie casou-se
com a filha de Yoritsuna.