Tadaakira rose through the ranks within the shogunate after beginning as a personal servant to the young shogun Tokugawa Ienari. As the threat of Russian incursions and other foreign concerns had eased somewhat since their crisis point in the first decade of the 1800s, Mizuno placed greater focus on domestic concerns. He revived policies of currency debasement, abandoned decades earlier, in order to help pay for, among other things, arranging marriages between Ienari's more than twenty children and members of daimyô households, and took various steps to ease the burden of coastal defense obligations for the daimyô. In 1821, he restored the Matsumae clan to their position overseeing matters on Ezo (Hokkaidô), and in 1820 and 1823 respectively lifted the burdens on Aizu and Shirakawa han for the defense of Edo Bay, placing the core of those responsibilities under direct shogunate control. Though initially aimed at centralizing control over preparedness, and ensuring that coastal defenses would be maintained more consistently in the long-term, in the end, the shogunate was quite lax in maintaining these defenses, leading to its rather unprepared state in the 1850s.
Mizuno was also responsible for the Edict to Repel Foreign Vessels (ikokusen uchiharai rei) promulgated in 1825 after foreigners landed on Takarajima in Satsuma domain, and on the coast of Mito han. This constituted a standing order to repel any foreign ships - including Dutch ships appearing anywhere distant from Nagasaki - with force. However, historian Mitani Hiroshi cites prominent shogunate officials as believing that even the use of force could not lead to full-on war, given the great distance of Japan from Europe; they believed that the incursions they had seen were isolated incidents of piracy, and would not be backed by national governments hesitant to bother engaging in wars fully halfway around the planet.
- Mitani Hiroshi, David Noble (trans.), Escape from Impasse, International House of Japan (2006), 16-18.