This is getting a bit redundant, since Rinyu Kanko (the corporation that run the Kurodake Ropeway website) have updated their website and it’s now easy to navigate in English, but here are the closure dates for Kurodake this winter:
The ropeway is closed from the 6th to the 31st of January (the chairlift is also closed for this period, since you need to ride the ropeway to get to the lift). It reopens on Saturday the 1st of Feb.
The chairlift is closed for another three weeks, until the 21st of February.
Plan your touring in the alpine above Sounkyo for February, and plan your big days for the last week of Feb and March.