Arai had worked in the Ministry of Foreign Affairs and in the office of former Governor of Hokkaido Takahiro Yokomichi, before resigning in 1993 to run in that year's general election.

[2] Arai managed to win a seat in his native Hokkaido and entered the House of Representatives, marking the start of his political career.

As his vote share was still considerably high in the races he lost, he always managed to return to the diet via the PR list.

He quit his seat mid-term in 2007 to run for the 2007 Hokkaido gubernatorial election against incumbent Harumi Takahashi, but lost.

Two years outside Parliament, he ran again in his old seat in 2009, defeating incumbent Gaku Ishizaki by a large margin in an election that brought his party into government.