The numbers are calculated by market sources, as cited by Reuters. This just adds to the one on Friday as noted here. But if you look at where USD/JPY is trading now (near 149.00), one can easily ask what intervention? ¯_(ツ)_/¯
For some context, Japan’s FX reserves stood at about $1.23 trillion at the end of September, according to official reserves data. So, they definitely still do have plenty of ammunition left but do they really want to keep at this considering how ineffectiveness the latest attempts have been?