In the Mori family who successively served as goteni (doctor hired by the bakufu) for Lord KAMEI of Tsuwano Domain, his grandfather and father had both been adopted in the family as son-in-laws for lack of a male successor, so Ogai was the first heir born for a long time.
代々津和野藩主、亀井公の御典医をつとめる森家では、祖父と父を婿養子として迎えているため、久々の跡継ぎ誕生であった。