When staying in a hotel in the U.S. or other countries, it is customary to tip the bellman, housekeeping, and restaurant/bar staff. However, when you stay in a hotel in Japan, you do not need to tip the hotel staff. For example, if you ask housekeeping to bring you a new set of towels, you don't have to give them a tip, and you are not rude to them at all.
Of course, if you give the hotel staff a tip to express your gratitude, they will be happy to receive it.
But if they don't accept your tip, please don't be upset or discouraged because it may be a hotel employee policy or a Japanese sense of hospitality.