All together, seven DPJ Dietmen have formally or informally declared their candidacy to succeed Kan.
Mr Maehara is the best chance the DPJ has of somebody even approaching Mr Koizumi's stature.
His leadership win comes as the DPJ government, led by Yoshihiko Noda, faces low poll ratings.
The 96-seat DPJ only says it wants to win more seats than the LDP.
There is even speculation that the TPP decision could result in a breakup of the DPJ.
FORBES: Noda's "Nixon to China Moment," TPP and Japanese Politics
The DPJ's hopes of governing majorities in both houses would then be in jeopardy.
He has been a member of the DPJ since 1998, assuming a number of leadership roles.
Maehara is probably the DPJ politician with the highest general popularity and confidence in leadership ability.
Where the LDP looked after producers' interests, the DPJ says it will put consumers first.
Nagoya citizens not only gave Mr Kawamura three times the votes of his DPJ rival.
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Hideto Sakaoka, a 54-year-old company employee, says he isn't voting for the DPJ again.
Second, the DPJ flopped mainly because candidates backing better government and pro-market growth did especially well.
DPJ, along with many foreign investors, wants banks' solvency to be judged by stricter criteria.
Others want Mr Ozawa to act as mentor to the DPJ's huge cohort of wide-eyed freshmen.
The conservative Liberal Democratic Party (LDP), which the DPJ ousted in 2009, is grey and cynical.
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He believes that a pact with the conservative elements of the DPJ might make it achievable.
ECONOMIST: An unusual militancy is creeping into mainstream politics
In June his fiscal conservatism prompted more than 50 left-leaning lawmakers to leave the DPJ.
ECONOMIST: An unusual militancy is creeping into mainstream politics
DPJ, is no longer about whether to reform Japan in a more market-friendly direction but how.
DPJ's own secretary-general will also step down, and the blundering Mr Nagata is to quit politics.
The DPJ has won a string of local contests in recent weeks, with significantly increased turnouts.
The DPJ is led by Kan Naoto, whom opinion polls consistently show is Japan's most popular politician.
The LDP governed Japan for half a century before it was ousted by the DPJ in 2009.
By the first week of July the DPJ will hold an election to choose a new leader.
In a speech to DPJ members on Friday, Mr Kan said rebuilding the economy was his priority.
But Japan's problems are so ingrained that the DPJ has so far been unable to do much.
For the DPJ government the opposition's ineptitude has not mattered, so capable has it proved at self-destruction.
He'll be looking to build his relationship and his personal ties with the new DPJ government there.
But the electorate did not vote out the LDP in order to see the DPJ start emulating it.
The DPJ's pledge on taking office was to make policy decisions itself and ensure bureaucrats acted on those.
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