The reason behind Iesada's name change was because successive Edo Bakufu Shoguns (Ietsuna [家綱] TOKUGAWA, Tsunayoshi [綱吉] TOKUGAWA, Ietsugu [家継] TOKUGAWA, and Ieharu [家治] TOKUGAWA) whose names were formed with hen (the left-hand side [radical] of a Chinese character) were childless (a biological child) or even these Shoguns with biological children had died young.
これは名に偏のついた江戸幕府の将軍（徳川家綱、徳川綱吉、徳川家継、徳川家治）には実子がないか、いても早世した。