[2] In 1976, he joined the Kita Nagare-Yama Dojo in Chiba Prefecture and attained the rank of 1st dan black belt in a little over one year.

[5] In May 1992, Matsui opened his own dojo in Asakusa, Tokyo,[1][4] and was later appointed as a Branch Chief by Oyama.

[2][4] Reportedly, a letter by senior Kyokushin instructor Peter Chong noted that Matsui was surprised to hear that he had been appointed to succeed Oyama, but also that Oyama had earlier named Matsui before several other people as the leading candidate to succeed him.

Following a dispute over the veracity of Oyama's will, Kyokushin karate as an organization divided into three main groups, led by Matsui, Kenji Midori, and Yoshikazu Matsushima.

[7] Matsui is currently ranked 8th dan,[2] and leads one of the IKO groups, supported by Yuzo Goda, Bobby Lowe, Peter Chong, and Seiji Isobe.