In recent decades, by-elections for the National Diet have been either held either together with an upcoming general/regular election for the other house or in April or October. After Machimura's death, the by-election in the 5th district was initially planned for October 2015; but as a Supreme Court decision on the constitutionality of the 2014 House of Representatives election was pending, the scheduling of the by-election was suspended. By September 2015, it was clear that the Supreme Court decision would not come in time to schedule the Hokkaido by-election for October, so it was postponed to April 2016 and eventually scheduled for April 24.
The by-election was widely viewed as a litmus test for Prime Minister Shinzo Abe's controversial defense and social policies; some observers said that Abe might have dissolved the House for a double election in mid-2016 if the LDP lost the by-election. Opinion polls prior to the election showed that voters were primarily concerned with foreign policy and security issues, followed by welfare and childcare. Wada campaigned strongly on his position as a successor to his father-in-law Machimura, whilst also providing his twenty years of experience in a trading company as evidence of his ability to improve economic conditions and promote the export of Hokkaido's agricultural produce. Wada was well-supported by the LDP and Komeito during the campaign, with many prominent members visiting the district.
Nomination strategy fallout
In February 2016, DPJ Hokkaido proportional representative Takako Suzuki applied to leave the Democratic Party over the party's cooperation with the Communist Party in the 5th district by-election. Her father had already indicated support for Wada and was hinting at an explicit Daichi endorsement. The DPJ responded to Suzuki's request by expelling her from the party. In the succeeding vote on the budget for fiscal 2016, the younger Suzuki voted with the ruling parties.
Results
Wada won the election by a margin of 12,325 votes in what was described as a full-faced battle between the ruling and opposition parties, the first such contest since the 2014 general election. The turnout was 57.6% of the 455,262 registered voters in the district, a slight decrease from the previous general election. Wada described the campaign as a tough battle, focusing on improving the local economy and becoming a "salesman" for Hokkaido in his victory speech. Ikeda was quoted as saying she faced the contest with the intention of creating a society in which all people can feel safe, and that the result was disappointing.