Supercopa de Japón
At the start of the 2012 season, Sakai started the season well when he helped Kashiwa Reysol win the Japanese Super Cup by beating FC Tokyo 2–1 on 3 March 2012. Three days after winning the Japanese Super Cup, he scored his first goal of the season in the AFC Champions League, in a 3–2 loss against Buriram United. Sakai scored and set up the club's third goal of the game, in a 3–3 draw against Yokohama F. Marinos in the opening game of the season. He continued to regain his first team place for the side this season, playing in the right–back position. His third goal of the season then came on 17 April 2012, in a 3–1 loss against Guangzhou Evergrande Taobao in the AFC Champions League. A month later, on 17 May 2012, Sakai set up two goals, in a 2–1 win over Cerezo Osaka. His performance attracted interests from clubs in Europe, mostly Germany, as the season progressed. With his move to Hannover 96 reached an agreement, Sakai made his last appearance for the club, which came on 30 June 2012, in a 6–2 win over Gamba Osaka. After his departure, he was given a farewell sendoff following an end of Kashiwa Reysol's match. Despite missing out one match by the time of his departure, Sakai went on to make 23 appearances and scoring 3 times in all competitions this season.