The headline reads that the US camp made it seem like it will consider the idea of joint FX intervention positively amid a meeting between Japan finance minister Suzuki and US Treasury secretary Yellen earlier. The details of the meeting can be found here.
I'd say this is more of a verbal threat more than anything else for now. Ideally, Japanese officials would want a slower decline in the yen but I don't believe we're at the stage where both sides will agree to any major intervention.
For some context, intervention to buy up the yen has been rather rare historically. The last time that happened was all the way back during the 1998 Asian financial crisis. And even then, the intervention efforts were rather futile as USD/JPY still rose to nearly 148.00 after.
As for the way that they would conduct the intervention, it would be simply just tapping into its reserves to sell dollars to the market in exchange for the yen. Hence, given the size and nature of the intervention, it usually will require some coordination or approval from its US counterpart.
