Today the UJ has started. As you can see on the chart it will most likely fall over the course of a few weeks to a few months. On the chart it ends on December 17. The timing might be different this year as for every season there are new variables and values. This year we had the raging bull from mid April onwards which has tremendously delayed the process. It would not surprise me if the bull shows up again to disturb this process.
This analysis is focussed on the time it takes for USD to reverse as marked with time ranges for each season on this chart. Normally a reversal of the USD takes around 12 weeks from last steep incline to first steep drop after that to complete. This year I expect a delay of at least 2 weeks for the reversal, which was estimated with a delay factor derived from the time it took to reach halfway the reversal.
The catalyst for this year's UJ Seasonality process was exactly that what you mentioned, namely JPY devaluing as a seasonal activity, and its fall would have launched UJ into orbit, i.e. if USD not would devalue at the same time, and this is exactly an activity of UJ seasonality's process. See JPY weekly and monthly performance for the seasonal devaluation activity.
In a nutshell, this year UJ Seasonality process functioned as a catalyst for JPY Seasonality and as its activity if would devalue USD, so UJ would not have been launched.