Nikkei Press estimated the market share of music soft in Japan in 2015. The total sales were 286 billion yen in 2015. According to it, Avex has the biggest share (17%).
Figure: 2015 Music Soft Market Share in Japan
|Company||Market share (%)|
|Sony Music Entertainment||13.1|
Source is Nikkei Sangyo Shimbun newspaper, the article on 2016 July 25th.