Masami's place is great and arguably one of the most comfortable spots I stayed in during my entire trip. The bed was very comfy and once you got used to using the local trains, very conveniently located (~10 min from Shinjuku station). She stayed up late on my first night there to make sure I arrived even though I had several delays in flights and train issues that put me back a few hours. I absolutely loved the balcony and having a pair of house shoes I could take with me was such a nice touch (great snacks, btw!). Masami was even kind enough to let me send the rental wifi there in advance since my flight was too late to pick up at the airport. I will 100% look to see if her place is available on my next trip to Japan and recommend it to everyone!!
Pro-tip on arriving from Narita: take the NEX/train to Shinjuku. It's easiest if you walk outside Shinjuku station and go across the street to the local train area and find your platform for Hatagaya (#4) on the Keio New Line--there is more than one platform for that line so pay attention to google maps! And make sure you have Suica card to scan in and out; the JR pass doesn't work on local trains in Japan.