The place was incredibly nice! Very large by Tokyo standards and a beautiful apartment. I went in a group of three, and it felt spacious; there is a large living room (with a european-style dining table), a separate kitchen, a bedroom with two beds (I think both bigger than twin-size but less than full-size), and also a room with tatami mats. I slept in the room with tatami mats and the futon that Sachie provided was very comfortable.
One thing to keep in mind is that there is a washer but no dryer. This is standard in Europe/Japan, but might take some Americans by surprise. We went in March and drying was no problem; we hung a bunch of clothing on hangers in the living room (there is a convenient piece of furniture for that) and everything was dry within 36 hours.
Sachie is an incredibly communicative host. She responded to most messages within an hour, and she lives right downstairs, so is easily able to help with anything that comes up.