Koizumi was prime minister several years ago, and he was very popular with the people. He has a rather charismatic quality about him, like Ronald Reagan or Bill Clinton.
What’s ironic is that Koizumi is the same party as current leader Abe, a party that supports nuclear power, and also a party that is considered to be quite conservative. (Sort of Japan’s version of the Republican Party of the United States.) (Koizumi’s switch to anti-nuclear feelings is recent, according to the article.)