Inui was the All Japan High School Soccer Tournament Letterwinner in 2006 when his high school, Shiga Yasu HS, won the tournament. In 2007, Inui joined Yokohama F. Marinos of the J. League Division 1 and made his debut as a professional against Yokohama F.C. in a league match on 10 March. However, he failed to find a regular spot at Marinos and was loaned to then J. League Division 2 Cerezo Osaka in June 2008, earning himself a permanent move at the end of the season. In July 2011, Inui made the jump to Europe, joining Germany's VfL Bochum. He made his debut in the 2. Bundesliga, when he started in a 1–2 home defeat versus FC St. Pauli on 13 August 2011. In July 2012, Inui signed a three-year contract with newly promoted Bundesliga club Eintracht Frankfurt after impressive performance in the German second tier.
On 26 August 2015, Inui was transferred to La Liga side SD Eibar for a then club record fees of € 300,000, after agreeing to a three-year contract. He became the first Asian player to play for the club. On moving to Eibar, Inui said, “It was always my dream to play in the Spanish league one day. It’s been my dream since I was a child and now it’s come true”. Takashi made his debut for Eibar on 23 September 2015, starting and providing one assist in a 2–2 draw against Levante. He scored his first league goal for Eibar on 10 January 2016 in a 2–1 win against RCD Espanyol, scoring the first goal in the 15th minute of game and also providing assist for second goal. In April 2017, as the club was chasing a UEFA Europa League place, he was controversially called back to his homeland by Japan's prime minister to serve as a delegate for the visit of King Felipe VI of Spain to Japan. On 21 May 2017, Inui became the first Japanese footballer to score against FC Barcelona, sniping the ball via cross-bar behind Ter Stegen, twice.
On 1 June 2018, upon expiration of his Eibar contract, Inui joined Real Betis on a free transfer for a three-year deal. He made his debut for Betis on August 17 2018, coming on as a substitute for William Carvalho for the last 25 minutes in 3–0 loss against Levante.
The following 24 January, after being sparingly used, he moved to fellow league Deportivo Alavéson loan until the end of the season. He made his debut for Alavés on 11 January 2019 in a 2–0 win Levante. He scored his first goal for Alavés on March 2 2019 in a 2–1 victory against Villarreal.
Return to Eibar
On 24 July 2019, Inui returned to Eibar on a three-year deal, for a fee of € 2 million.
International career
Inui made his full international debut for Japan on 20 January 2009 in a 2011 AFC Asian Cup qualification against Yemen. In May 2018 he was named in Japan's preliminary squad for the 2018 World Cup in Russia. On 24 June, Inui scored his first World Cup goal in a 2–2 draw over Senegal during their second group stage match of the tournament. Inui went on to score another goal and registered an assist in the tournament.
