It's now legal to house share in Japan. "Airbnb Gets Green Light in Japan With Home-Sharing Law's Passage by Pavel Alpeyev June 9, 2017, 12:21 AM EDT The law limits stay in private homes to 180 nights a year Airbnb hosts will have to register with local governments Airbnb Inc. will now be able to operate in Japan without the risk of running into regulatory hurdles after the government passed a law that sets out rules for home sharing. Japan’s upper house passed a legislative bill on Friday that lets private homes rent out space to paying guests, while limiting total stays to 180 nights a year. The law requires providers of such accommodation to register with local governments and lets local authorities impose their own restrictions." https://www.bloomberg.com/news/arti...ight-in-japan-with-home-sharing-law-s-passage
It was never full-stop prohibited. Previously it was down to the ward level, whether they wanted to put up rules or not. I believe of the 23-wards, only one did (but that was just hearsay).