From mid-June of 2018, the law concerning guest houses in Japan changed.
Hosts or managers are required to obtain the following information about all guests who do not live in Japan:
This information is for MLIT-the Ministry of Land, Infrastructure, Transport and Tourism.
Your information will not be sold. It will only be used by MLIT.
You are legally required to give this information. Guest houses in Japan are basically being treated as quasi-hotels. So like hotels, they are required to gather this information from guests.
It seems it has actually been a requirement since 2005! But I was not aware of it until recently.