The Ninja House was a big part of what made our first trip to Japan so memorable. To basically have your own house (even if things are a bit tight) in walking distance (about 25 mins) to Shinjuku station is so invaluable, it can't be stressed enough. If you don't wanna walk, Keio New Line is about a 7 mins walk away and takes two stations to Shinjuku. The House is located in a quite residential area where you can't even feel what is going on "in town" just kilometer away. And you even get a terrace on the roof, another great perk barely mentionend in the listing (remember, it's a residential area, be respectful).
Shin was a great, uncomplicated host and responds to messages immediatley. Just know that the ground floor (and only the ground floor) can be a bit cold when the weather outside is as well, but theres lots of radiators to counter that. Be sure to check out Miki's around the corner!