AirBnB in Japan aren't actually hosted by the local population (read: Japanese) much. This sounds weird, but unless you find someone with a Japanese name, an actual picture of a Japanese person, a Japanese written description, the chances are astronomical that you've taken for the Chinese/Vietnamese/Philippines or otherwise SEA trap.
To give you a gross outline of how these things coke to be, there are Chinese/SEA people, who come to Japan after a long fight to get a visa (they mostly will either study Japanese 6 months or attend a short term exchange between universities). While in Japan they look for a largely cheap apartment and when they are at the end of their visa, they leave Japan but retain the apartment and ask their fellow countrymen, who are otherwise either unable to do this themselves and/or need some extra cash, to clean these apartments. For them, it's as purely for money as this will set them for life in their cheap(er) country.
Of course there is a huge secrecy. That's because it's mostly illegal (as the majority of apartments are not owned but rented) and there is no insurance coverage, let alone, if something happened they don't touch these people as they have left the country.
Japan of course hates these type of people with a passion. It's like finding a sushi restaurant abroad and thinking it's Japanese. Yeah... they are mostly not. And sadly people don't know the difference. It's just a cheap and terrible knockoff of Japan.
The more you know!
(I have worked and lived in Japan for several years and speak fluent Japanese)