Twitter Japan announced on the 2nd November that user growth had been 13% (+5 million) for the past 9 months, bringing the Japanese monthly active user count (MAU) to 40 million in September. This compares to Twitters MAU growth in the rest of the world, which is essentially flat.
In December 2015, Twitter Japan announced that 10% of MAUs were from Japan.
I have written on this topic several times on this blog. What I think is most important is that the features and characteristics of social media platforms are not dictated by what features they have and do not have, but instead are determined by the users themselves. Therefore, all the pundits that say Twitter should do this or Twitter should do that are essentially clueless because they only know how they or their close circles use Twitter, but are mostly blind to how other are using it. Analysing what features are available does not capture what people use a social service for, nor does it give you any idea of how people would use a new feature when available.
Social media needs social analysis. Furthermore, you need to analyse many societies and not one society.