To take over as the reign of a samurai family, a successor was required to notify and to be approved as the heir and son by the head family beforehand (the family of the Tokugawa Shogun was the head family of all the daimyo families).
武家の家督を継ぐためには、主家（大名にとっては徳川将軍家が主家ということになる）に事前に届出をして嫡子たることを認められる必要があった。