Answer
Matsui joined Slavia Sofia in 2015. He made his debut for the club in a 2-0 win over Lokomotiv Sofia on 16 August 2015. Matsui scored his first goal for Slavia Sofia in a 2-1 win over Cherno More Varna on 12 September 2015. He went on to make 26 appearances for the club in all competitions, scoring 4 goals.