By Linda Sieg
TOKYO (Reuters) - The first female leader of Japan's opposition Democratic Party, Renho, said on Thursday she was resigning after her party failed to capitalize on Prime Minister Shinzo Abe's sinking support rates and suffered a heavy defeat in a Tokyo election.
Renho, who was born to a Japanese mother and a Taiwanese father and goes by one name, had hoped to repair the party's image when she took over last September. Her party was battered by three years in power plagued by bickering, flipflops and unkept promises.
However, support for the Democrats remains well below 10 percent even though backing for Abe has slid to below 30 percent in some polls because of suspected cronyism scandals and a feeling among voters that he takes them for granted.
"I have decided that it would be best to have new leadership take over," Renho told a news conference.
"I was unable to demonstrate the power for the Democratic Party to become an alternative to the Abe cabinet, which appears to be a distorted administration," she said. A party election would be held promptly to replace her, she said.
Abe's Liberal Democratic Party (LDP) suffered an historic defeat at the hands of Tokyo Governor Yuriko Koike's Tokyo Citizens First Party in a July 2 Tokyo Metropolitan assembly election, where the Democrats took only five of 127 seats.
Renho, 49, was also plagued by a row that erupted when it was discovered last year that she held Taiwanese as well as Japanese citizenship.
Japanese law requires those with dual citizenship to choose by age 22 and, when opting for Japan, try to renounce the other nationality, although there is no penalty for not doing so.
She made part of her family register, or "koseki", public last week to prove she had renounced her Taiwanese citizenship and declared her choice of Japanese citizenship.
Renho told the news conference that the citizenship issue had nothing to do with her decision to resign.
The novice Democratic Party surged to power in 2009, ousting the long-ruling LDP with promises to put individuals ahead of companies and address social inequalities. Abe led the LDP to its own landslide victory three years later.
Although a Democratic Party-backed candidate won an election on Sunday for mayor of the northeastern city of Sendai, a Mainichi newspaper poll put support for the opposition party at a mere 5 percent, down three points from June.
(Additional reporting by Ami Miyazaki; Editing by Paul Tait)