A native of Kumamoto, Japan, Baritone Eijiro KAI holds both Bachelor and Master of Fine Arts degrees from the Tokyo National University of Fine Arts and Music (Tokyo Geijutsu Daigaku). He was awarded 1st Prize at the XXIX Concorso Lirica Italiana in Tokyo, Japan in 1998, 3rd Prize at the "VIII Concorso Internazionale per giovani cantanti lirici RICCARDO ZANDONAI" in Riva del Garda, and 1st Prize at the "10°Concorso Internazionale TITO SCHIPA" per giovani cantanti lirici in Lecce, Italy in 2002. In Tokyo, he made his New National Theatre Tokyo debut in January 2004 and NIKIKAI Opera-debut in February 2002. In May 2002, he joined "Seiji Ozawa Ongaku-juku". In April 2003, he joined the project again.
 He made his Wiener Staatsoper debut as Fiorello in Il Barbiere di Siviglia in September 2003, and performed as Schaunard and Marcello in La Bohème, Paolo in Simon Boccanegra, Schlémil and Hermann in Les Contes d'Hoffmann, Sciarrone and Angelotti in Tosca and Marchese in La Traviata, 1st Mate in Billy Budd, Sir Gualtiero Raleigh in Roberto Devereux. Le Comte de Toulouse in Jerusalem, Morales in Carmen, Belcore in L'elisir d'amore, Grégorio and Mercutio in Romeo et Juliette, Boroff in Fedora, Roucher in Andrea Chenier, Erster Schäfer in Daphne, Marullo in Rigoletto, Lescaut in Manon Lescaut. He is a member of Nikikai.