Hilton is celebrating its 50th anniversary in Japan by offering 50% discount for 50 hours at their 10 Japanese properties. This sale starts on Tuesday June 25 at 8PM Japanese time and ends on Thursday 27th at 10PM Japanese time. The discount is eligible for stays up to March 31, 2014. This offer requires prepayment and is non-refundable/non-cancelable.
Edit: I have corrected the starting and end dates of this sale.
Note that the website for this offer is entirely in Japanese, but what I am able to gather just staring at the YEN pricing, the prices are quite attractive.