[1][2] On 1 August 2012, United Nations Secretary-General Ban Ki-moon announced Kan would be one of the members of the UN high-level panel on the post-2015 development agenda.

[5] He actively engaged in civic grassroots movements for years and also served on election campaign staff for Fusae Ichikawa, a women's rights activist.

[7] While serving in this position he gained national popularity for admitting the government's responsibility for the spread of HIV-tainted blood in the 1980s and directly apologized to victims.

[citation needed] In September of the same year, after having left cabinet, Kan founded the Democratic Party of Japan along with Yukio Hatoyama.

[7] In 1998, his image was affected by allegations of an affair, vigorously denied by both parties, with a television newscaster and media consultant, Yūko Tonomoto.

The initial intent of the party was to offer places of activity for the Japanese baby boomers – 2.7 million of whom began to retire en masse in 2007.

[16] Foreign Minister Katsuya Okada and Land and Transport Minister Seiji Maehara, though once considered to be possible successors to Hatoyama, announced their support for Kan.[17] Kan, at the age of 63, won the leadership of the DPJ with 291 votes to 129, defeating a relatively unknown Ozawa-backed legislator Shinji Tarutoko, 50,[16][18] who was leading the environmental policy committee in the lower house of the Diet.

[28] China protested the arrest, as it claims the islands as part of its sovereign territory, and demanded the unconditional release of the captain.

[31] The Kan government intervened in mid-September to weaken the surging yen by buying U.S. dollars, a move which temporarily relieved Japan's exporters.

That evening, following an order from METI Minister Kaieda to begin pumping seawater into the plant for emergency cooling purposes, Kan expressed concern that the seawater injection plan may lead to re-criticality, in response to which TEPCO directed plant manager Masao Yoshida to stop pumping (an order which Yoshida tacitly ignored).

Several weeks later, Shinzo Abe circulated information that Kan had ordered pumping to stop, which the Yomiuri Shimbun and other news outlets reported as fact, and opposition leader Sadakazu Tanigaki accused the government of causing the Fukushima meltdowns.

While this move initially antagonized TEPCO, it was later positively evaluated as improving communications between the plant operator and government agencies such as the Self-Defense Forces and Tokyo Fire Department.

Kan slept in the Prime Minister's Office and did not return home for an entire week after the disaster struck; he wore blue coveralls instead of a suit until the end of March.

[38] In May, he ordered that the aging Hamaoka Nuclear Power Plant be closed over earthquake and tsunami fears, and he said he would freeze plans to build new reactors.

[39] Despite falling popularity, Kan rejected calls to step down while the country continued to suffer from the earthquake, tsunami, and nuclear crises of spring 2011.

One year into his premiership on 2 June 2011, Kan proposed his resignation, hours before the Diet put forward a vote of no-confidence.

[42] In August, Kan removed three of Japan's top nuclear energy officials in effort to break ties between government and the atomic industry.

[43] When interviewed in 2012, after resigning as prime minister, Kan said the Fukushima accident made it clear to him that "Japan needs to dramatically reduce its dependence on nuclear power, which supplied 30 percent of its electricity before the crisis, and has turned him into a believer of renewable energy.

[65][66] Kan was portrayed by Shirō Sano in the 2020 film Fukushima 50, and by Fumiyo Kohinata in the 2023 Netflix series The Days (in which his name was changed to Shinji Azuma).

The media and public opinion, manipulated by the latter, were totally hostile to the Prime Minister, accusing him of having aggravated the accident and amplified the damage.

Faced with this rejection, I was plagued by anger and disgust as they led me to make this film to put things in order.The reactors’ accident could, in the worst case, have caused the evacuation of the entire population living within a radius of 250km, including Tokyo, a total of 50 million people.

[67]Naoto Kan has an important cameo appearance in the 2023 Documentary Film SOS: The San Onofre Syndrome directed by James Heddle, Mary Beth Brangan and Morgan Peterson.

On a recent interview producer Mary Beth Brangan stated that it was the Fukushima accident what set her and her life partner James Heddle into the making of that film.

In his concluding statement Prime Minister Kan stated: "After Fukushima, my whole mindset about nuclear power has changed 180 degrees...