This Airbnb was comfortable for a solo trip and would be fine for a couple — if you don't mind sleeping in two single beds next to each other. The draw for me was the neighbourhood and it did not disappoint. Quiet when you need it but with lots to do around and very close to the subway station. I mostly walked to Shinjuku station but that's a good 20-minute brisk jaunt away. Otherwise, I would grab the subway from Shinjukugyoenmae (3 minutes from the apartment) and head in whichever direction I needed. Easy-peasy.
The park (the gyoen in Shinjukugyoen) is quite nice but it'll cost you 500 yen. I mostly ate out but the kitchen basics in the apartment are enough to prepare light meals.
Tall and/or bigger folks might struggle in the bath/shower so something to consider if you're north of 6ft tall or broad-shouldered. The same goes for the two single beds. They are no doubt sturdy but they are on the smallish side.
An important note here: Shinjuku Nichome is only a few minutes walk from the apartment and is the centre for all things gay. With hundreds of bars, restaurants and, I'm guessing, saunas, you will love it here.