Status of the lord of Mito Domain was different from other daimyo (Japanese feudal lords), and they were required to Jofu (a Daimyo feudal lord's retainer who remained permanently in the Edo with the lord's and their own family in the Edo period) in stead of Sankinkotai (a system under which feudal lords in the Edo period were required to spend every other year in residence in Edo) and they were more likely to be the assistant for shogun.
これは、水戸藩主の地位が他の大名と違って、参勤交代せずに常に江戸に留まる定府が義務付けられていたこと、将軍の補佐役としての色彩が強かった。