[3][4] He has also been criticized for misogynistic views expressed in the past, and caused controversy when he invited women to "look, but not talk" at key party meetings.

While attending Gobō Middle School, he participated in an extracurricular debating society, where he addressed the human rights issues facing the Burakumin, citing The Broken Commandment, a novel by Tōson Shimazaki.

He immediately entered politics, working as secretary for Saburo Endo, a Diet member from Shizuoka who was serving as the Minister of Construction.

[2] In 2005, Prime Minister Junichiro Koizumi tapped Nikai to head the Diet committee in charge of the privatization of Japan Post.

[citation needed] Following the general elections of that year, on 31 October, Koizumi selected Nikai to head the Ministry of Economy, Trade and Industry, traditionally one of the most highly valued cabinet portfolios.

[8] On 25 March 2024, Nikai announced that he would not run for reelection in the next House of Representatives election after his Shisuikai faction disbanded in the wake of the 2023–2024 Japanese slush fund scandal.

Nikai also assumed political responsibility for the scandal after Shisuikai failed to declare 35.26 million yen ($233,000) in revenues from ticket sales of its fundraising parties from 2017 to 2022.