A perfect little base for exploring the city from Kōenji (and exploring Kōenji itself), <5 minutes walk from Kōenji station (about 10-15 minutes train ride to Shinjuku). This is a compact apartment with everything you need, and a comfortable 2-person futon bed in the loft. Self check-in was easy, and Tomomasa sent helpful instructions for finding the building.
Things to be aware of: (1) the ladder up to the loft is fairly long and steep, so best for spry younger people; (2) if you're American, just be aware that Japanese apartments are much smaller than we're accustomed to - the bathroom in particular may feel cramped. This is typical in my experience, and any apartment you stay in is likely to be similar.