Bruised by the resignation of his finance minister, close ally Shoichi Nakagawa, Japanese Prime Minister Taro Aso may be forced to step down, like his two predecessors.
Following are some possible candidates who may replace Aso as leader of the ruling Liberal Democratic Party (LDP), and premier.
SHIGERU ISHIBA, 52
Currently serving as agriculture minister, former defense minister Ishiba is known for what media call a "geeky" knowledge of security issues and has written several books on defense.
Ishiba gained a reputation as an unflappable debater when the LDP wrestled with the powerful opposition over the renewal of a legal mandate for marine refueling in the Indian Ocean in support of U.S.-led military operations in Afghanistan.
He stood against Aso in a party leadership race in September.
NOBUTERU ISHIHARA, 51
A reporter turned politician, Ishihara is the son of outspoken nationalist Tokyo governor Shintaro Ishihara, but has more moderate views. He was one of five candidates, along with Aso, who ran in the September's LDP party leadership race.
An advocate of sweeping reform of the bureaucracy, he has served as transport minister and minister for administrative reform. He was one of several young ruling party lawmakers who worked on steps in 1998 to revitalize Japan's crisis-hit financial sector and is well-versed in economic policy.
YURIKO KOIKE, 56
A former TV announcer fluent in English and Arabic, Koike served briefly as Japan's first woman defense minister in 2007.
She ran in the ruling party leadership race last year in a bid to become the country's first female prime minister on a platform pledging to stick to popular former premier Junichiro Koizumi's market-oriented reforms.
As environment minister, she launched a "Cool Biz" campaign to encourage office workers to dress more casually in summer to cut down air-conditioner use and help fight global warming.
Koike has a record of switching parties. Her career began in the opposition and she was once a protege of Ichiro Ozawa, now leader of the main opposition Democratic Party.
MASAHIKO KOMURA, 66
Komura has served in the past as foreign, justice and defense minister and is known for his ability to blend into the background while offending few. He has advocated closer ties with regional rival China.
In a long government career, he has also headed then-Economic Planning Agency. A qualified lawyer, Komura holds a qualification in kung fu.
YOICHI MASUZOE, 60
Masuzoe, currently health and welfare minister, is a multi-lingual former scholar versed in international and domestic politics. He first won an upper house seat in 2001.
His mother suffered from dementia in the years leading up to her death, and Masuzoe has written a series of magazine articles about his experiences caring for her.
Though widely seen as competent and hardworking, he has struggled in his current post to reform the national pension system, which has been found to be riddled with errors and fraud.
SEIKO NODA, 48
Currently cabinet minister in charge of consumer affairs, Noda was once tipped as a possible first female prime minister.
She was appointed posts and telecommunications minister at the age of 37, but lost prominence after speaking out against Koizumi's postal reforms.
Noda left the LDP to stand as an independent in a 2005 election Koizumi called to resolve the subsequent row that split the party, but has now returned to the fold.
SADAKAZU TANIGAKI, 63
Tanigaki, who has served as finance minister and transport minister and is now deputy tax panel chief of the ruling Liberal Democratic Party, is well-versed in economic policy.
A graduate of the elite Tokyo University and a former lawyer, he has said Japan needs to raise its consumption tax to fix its huge public debt.
In an interview with Reuters on February 5, Tanigaki said rapid rises in the yen may hurt Japanese exporters, but the currency's level around 90 yen per dollar was not out of line with economic fundamentals.
Tanigaki is seen as a relative dove on foreign policy.
KAORU YOSANO, 70
Yosano, who came second to Aso in the race to become prime minister last year, took on the finance and banking supervision portfolios after Nakagawa resigned and retains his role as economics minister.
A fiscal hawk and tax expert who has shown flexibility about spending as the recession has deepened, Yosano has called for a higher sales tax rate to help fund social security costs.
In late 2006, Yosano resigned from the post of chairman of the ruling party's powerful tax panel due to cancer of the pharynx. After surgery to remove a tumor and some time off, he returned to politics and has served in the past two cabinets.
The grandson of two well-known poets and a graduate of the prestigious University of Tokyo, Yosano is a master player of Japan's chess-like game of Go.
(Reporting by Isabel Reynolds and Yoko Nishikawa; Editing by Valerie Lee)