It doesn't specifically say it is for Japanese residents only, but the language barrier effectively makes it so. The Sheraton Yokohama similarly sells rooms listed as singles on spg.com as suitable for couples on its Japanese website...
Apart from the 'Welcome to Hilton' rate, there is no mention of those rates being Internet specials.
I would try calling. If they don't give you the rate you want, politely hang up and go to the japanese website with the help of
http://babelfish.altavista.com/ , which now has (limited) Japanese functionality (full paragraphs come out funny, but inputting single words and using creative grammar, one can understand most sentences).
When you do get to the booking form (second orange button from the right on the rate descriptions), you are asked:
- date
- number of rooms
- number of guests
Next screen is for personal data:
* first box: rate confirmation
* 2nd box: sign-in for Hilton Online Network members (skip)
* 3rd box: data for non-members. Enter:
- surname/name in Chinese characters
- surname/name in hiragana (try roman characters)
- email address (twice)
- phone number
*the above fields are required*
- zip code
- street address
- check HH level in blue box (basic >...> diamond)
- enter HH number
Last box: optional info
- arrival time
- arrival by private car or public transp.
- contact by phone or email
- check for non-smoking room
All of the rates listed are applicable, but may not be available. Start by the lowest and work your way up if your date is not available.
FYI, there is a Y4,200 rate until the end of June, which may be available if you call them at 9pm on the day of arrival.
PS. to see how their booking form looks like, try the lowest rate before 6/20. Later dates yield a 'not available' answer.