嗣ぐ[tsugu] to succeed (someone in a business or inheritance)
継嗣[keishi] successor
後嗣[koushi] heir
嗣子[shishi] heir
嫡嗣[chakushi] legitimate heir

天津日嗣[amatsuhitsugi] imperial throne
世嗣[yotsugi] heir
養嗣子[youshishi] adoptive heir
皇嗣[koushi] Crown Prince
皇帝の嗣[kouteinoshi] Emperor's heir