Airbnb has the wrong business model for Japan, try these instead:

Ryokan 旅館 are hotel-like accommodations that provide guests with the full Japanese treatment -- onsen, tatami, cuisine, gorgeous country settings. If you want to be pampered and have a luxury experience, this is for you.

Minshuku 民宿 are family-operated bed and breakfasts, where you are actually staying in the house where the host (and cook) reside. If you want to experience true home cooking, and aren't afraid to communicate using simple Japanese this is for you.

Minpaku 民泊 are the Airbnb-style "Private Lodgings", essentially the same as a vacation rental elsewhere in the world. If you want to be in the countryside, do all your own grocery shopping and cooking, and are willing to miss out on the cultural exchange, this is for you.