I stayed at Riko-san's apartment for about a month.
The location is fantastic, right around the corner from Nakameguro station and right off the river.
Riko-san was responsive throughout the stay with any questions and even offering in-person help if I needed it.
The apartment building is very old by Tokyo standards, built in 1961 according to real estate listings. Inside, some things are renovated and whether guests feel comfortable is more about their standards and expectations. For foreign tourists it may feel more "authentic".
I gave an overall 3-star rating, however, because I did not feel safe in this building. There were four earthquakes during my stay, one of which was the largest Tokyo has experienced in many years. I do not have confidence in the earthquake safety of the building. The earthquake shook the building so strongly that all the cabinets in the kitchen shook open and many things fell over including a large mirror. I have lived in Tokyo for 6 years and experienced many earthquakes inside newer reinforced concrete buildings and felt much safer.
So I just wanted to mention this as a "at your own risk" kind of warning to other potential guests. Airbnb does not post earthquake safety information of the homes rented in Japan as far as I can tell. When the next big earthquake comes to east Japan I would not want to be inside this building.