Yuriko Koike, a Kansai native who had represented various Kansai districts in the House of Representatives since 1993, was parachuted into the Tokyo 10th district by LDP Prime Minister Junichiro Koizumi for the 2005 general election following the defection of Koki Kobayashi [ja], who had held the seat for the LDP since its creation in 1996. Koike defeated Kobayashi in the 2005 election but lost to Democratic Party of Japan (DPJ) candidate Takako Ebata in 2009. Koike regained the seat from Ebata at the 2012 election and retained it at the 2014 general election.
Tokyo governor Yoichi Masuzoe resigned in June 2016 due to various problems with his use of public funds. On 29 June Koike held a press conference and stated her intention to contest the gubernatorial election to replace Masuzoe that was scheduled for 31 July.[2] On 5 July Koike met with Nobuteru Ishihara, the head of the LDP's Tokyo branch, to formally request the LDP's endorsement. However, with the branch planning to endorse former Iwate Prefecture governor Hiroya Masuda, Ishihara's response to Koike was that the branch would make a decision after the national House of Councillors election on 10 July.[3]
^"小池元防衛相が出馬表明＝都知事選" [Former Defence Minister Koike intends to contest Tokyo gubernatorial election]. Jiji (in Japanese). 29 June 2016. Archived from the original on 13 August 2016. Retrieved 13 October 2016.
^"石原氏、会談で小池氏に「参院選後に結論出す」" [Ishihara meets with Koike "Decision after the House of Councillors election"]. Yomiuri Shimbun (in Japanese). 5 July 2016. Archived from the original on 16 August 2016. Retrieved 13 October 2016.
^ ab"平成28年10月23日執行 衆議院議員補欠選挙（東京都第10区） 立候補者一覧" [23 October 2016 Tokyo 10th District By-Election List of Candidates] (PDF) (in Japanese). Tokyo Metropolitan Electoral Commission. Retrieved 12 October 2016.
^"【衆院ダブル補選】東京１０区は小池百合子氏支援の自民・若狭勝氏が勝利 福岡６区は鳩山邦夫氏の次男が分裂選挙を制す" [(House of Reps. Double By-Election) LDP's Masaru Wakasa supported by Yuriko Koike wins Tokyo 10th, Kunio Hatoyama's second son victorious in divisive Fukuoka 6th election (Page 2)]. Sankei Shimbun (in Japanese). 23 October 2016. Retrieved 25 October 2016.
^"【衆院ダブル補選】東京１０区は小池百合子氏支援の自民・若狭勝氏が勝利 福岡６区は鳩山邦夫氏の次男が分裂選挙を制す" [(House of Reps. Double By-Election) LDP's Masaru Wakasa supported by Yuriko Koike wins Tokyo 10th, Kunio Hatoyama's second son victorious in divisive Fukuoka 6th election (Page 1)]. Sankei Shimbun (in Japanese). 23 October 2016. Retrieved 25 October 2016.
^"衆議院（小選挙区選出）議員補欠選挙 候補者別得票数（全候補）" [House of Representatives (Individual Districts) By-Election Results by Candidate (All Candidates)] (PDF) (in Japanese). Tokyo Metropolitan Electoral Commission. Archived from the original(PDF) on 25 October 2016. Retrieved 25 October 2016.
^"衆議院（小選挙区選出）議員補欠選挙 投票結果 （国内＋在外）" [House of Representatives (Individual Districts) By-Election Turnout (Inside and Outside Japan)] (PDF) (in Japanese). Tokyo Metropolitan Electoral Commission. Archived from the original(PDF) on 25 October 2016. Retrieved 25 October 2016.
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