It appears that today is the last day of operations for the JNR era 205 Series EMU on Musashino Line with the last set from Keiyo Yard (M20) being removed from service after today, which probably meant the conversions of E231-0 and E231-500 EMUs for Musashino and Chuo-Sobu Lines are near or at completion
https://www.youtube.com/watch?v=hnGpuov1zG8https://www.youtube.com/watch?v=DfMG_ppjDcM