In general, it's a fact that hotel prices usually do change with the season, day of the week, holidays, etc. I completely agree.

But I just looked at about 30 random dates over the next four months at this property and could not find a day where the lowest price for a room was over 5300 yen. It appears that these rates are "special discounts" off their "normal" rates (perhaps the 10,000 yen you mentioned). Interestingly, every single day that I looked at they offer these "special discounts" on their rooms. Truth be told, I think if they charged anything too much more than this, they might have a difficult time staying in business.

Another point of interest is that no rooms whatsoever were available 120 days out. Either this property only accepts reservations on their website up to 4 months out, or is going out of business four months from now.