Koichi's place is great! Very spacious (I traveled alone, but the space is also quite enough for a couple, lots of storage room for luggage as well). Very clean, lots of towers you can use. The location is very convenient too, less than 10 minutes walk from heart of Shinjuku.
Also, Koichi is a wonderful host! He offered to pick me up at Shinjuku station. When I left, he also helped with my luggage (which was a lot!) to the train station to Narita. He's also familiar with everything there, I found his suggestions on restaurants, shopping are better than the tips online.
Overall, it's been a wonderful stay and I'll definitely book again next time I come!