From the official webpage for the event in 2015
The landmark Redbrick Warehouses in Yokohama (akarenga 赤レンガ) are running a number of Christmas events this holiday season, including the chance to meet Santa Claus.
Redbrick Warehouse Santa Dates
If you are looking to visit Santa on a weekday near Tokyo, this might be the place for you. As all the Santa dates at the Redbrick Warehouse in Yokohama are weekdays. He will be there on December 1st, 5th, 7th, 12th, 14th, 18th and 20th. They do not provide specifics of how or times of when you can meet him, but in previous years he was walking around the redbrick warehouses. If you can find him, you can get your photo taken with him.
Christmas Events at Redbrick Warehouse
Other Christmas events at the Redbrick warehouses include a Christmas market which started on November 25th, an art rink from December 2nd to the 18th, and lots of workshops. There are other events on the days that Santa isn’t there such as Christmas songs on the 4th, 8th and 13th. And on the 6th and the 13th there is evening entertainment.
For more information in Japanese: