Nikkei Press estimated the market share of credit card firms in Japan in 2015. According to it, Mitsubishi UFJ NICOS has the biggest share (12.3%). The industry-wide total billings were 43 trillion yen in 2015.
Figure: 2015 Market Share of Credit Card Firms in Japan
|Firm||Market Share %|
|Mitsubishi UFJ NICOS||12.3|
|Sumitomo Mitsui Card||11.7|
Source is Nikkei Sangyo Shimbun newspaper, the article on 2016 July 25th.