Hi Senta, thanks for the awesome stay!
Everything was good when it comes to location. There are staff on ground level that can assist you during office hours as well. Eg. They gave me additional pillows and water if you need more. Furthermore, After we check out, they even allowed me to leave the luggages as my plane is only later at night.
As for the location, It is 5mins from Okubo station which is 1 station away from Shinjuku! Also Just 1 station away or 10mins of walking, there is also Shin-Okubo station. It is a korea street where you can settle all your korea cravings (it is like a mini korea there). The Donki nearby is crazily huge!
Just abit of a setback is that there is no lift but they have staff that can help you to carry together. If you have a lot of luggages might be something to consider.