The music he often listens on his Walkman is Japanese pop music. His favourite artists are pop group Mr. Children and singer Yui. (Mr. Children, or Misuchiru, is a very popular group in Japan but they're not exactly a favourite among youngsters in Kei's generation. Apparently it's his father's influence that he became their fan, according to what I read some time ago.)
WOW, Mr Children, my all-time favourite Japanese band.
Ooopsss, seems like i am exposed my age already.
Bet he has the latest album Supermarket Fantasy.