As early as 1839, he petitioned the shogunate to take action to defend the northern borders against Russian encroachment. Five years later, he had fallen out of favor with the shogun & with the rôjû; after being found to have been stockpiling weapons in excess of limits set by the shogunate, he was forced to relocate himself, his family, and many of their attendants and retainers, from his domain's Koishikawa mansion to one at Komagome, another district of Edo.
In 1853, Nariaki was appointed by the shogunate to oversee decisions concerning the naval defense of the realm. He was an avid supporter of maritime restrictions, opposing Abe Masahiro's decision to give in to the demands of Commodore Perry and Hotta Masayoshi's signing of the Harris Treaty, and expressing his support for Emperor Kômei's opposition to acceding to the terms of that treaty. Nariaki is thus strongly associated with the sonnô jôi movement, though his involvement was chiefly in negotiations and disputes amongst members of the highest levels of samurai and Imperial Court society.
When Shogun Tokugawa Iesada was on his deathbed in 1858, Nariaki attempted to have his seventh son, Tokugawa Yoshinobu, named Iesada's heir. His defeat by the opposing faction in this succession dispute meant that he was once again out of favor with the dominant ruling faction, and so he returned once again to the Komagome mansion. Rumors that he might be ordered to commit suicide led many of his retainers to prepare themselves to defend their lord against messengers from the shogunate carrying such an order; these tensions were defused, however, as the shogunate instead ordered Nariaki to retire to Mito.
In 1860, Tairô Ii Naosuke was assassinated by a group of rônin from Mito and Satsuma domains. While Naosuke was certainly among Nariaki's chief political rivals, and represented political stances and policies both Nariaki and these sonnô jôi rônin were very much opposed to, it remains unclear whether Nariaki was involved in, or even aware of, the assassination plans.
That same year, Nariaki saw one more of his political plans go awry; he had arranged with Iesada that Iesada's successor as shogun, Tokugawa Iemochi, would marry one of Yoshiko's princely (Imperial) relatives. This would have enhanced the prestige and influence of Nariaki's own family. However, it was announced in 1860 that Iemochi would instead marry Kazu-no-Miya, a younger sister of Emperor Kômei, something of which "everyone in Mito disapproved."
Nariaki died later that year, and was succeeded as lord of Mito by his eldest son, Tokugawa Yoshiatsu.
- Plaques on-site at the former site of the Mito Kyoto mansion.
- Anne Walthall, "Nishimiya Hide: Turning Palace Arts into Marketable Skills," in Walthall (ed.), The Human Tradition in Modern Japan," Scholarly Resources, Inc. (2002), 45-60.
- David Howell, "Is Ainu History Japanese History?," in ann-elise lewallen, Mark Hudson, Mark Watson (eds.), Beyond Ainu Studies, University of Hawaii Press (2015), 107.
- Walthall, 49.