I am staying here as part of a tour group. After the match we returned hoping to get a drink. The top floor bar was full and people were queuing. The lobby bar, however, was practically empty. The sign, see photo, suggests that it's open till 11pm. The photo was taken at 10pm! So, they don't want us here.
Earlier we went to take advantage of a special offer to watch the two earlier games on the big screen (they had a big screen in the Banqueting Room with a bar and snacks) before heading to the stadium.
First match kicked off at 1.45pm. They were going to open the Room at 3pm! We made alternative arrangements.
This is Japan's biggest sporting moment until the Olympics next year and the whole country, with the exception of this hotel, has embraced it. By all means stay here but don't expect them to understand or recognise why you're there.