No reservation places
We're planning to try and get into Ahiru Store, which I understand is not always possible. In case it's extremely crowded, can you recommend places that we could get into with no reservations, preferably not all the way across town (although even if they are across town it might be fine).
Well that's a pretty broad request seeing you haven't specified the kind of food you want, or what day of the week you intend to go out.
Given you mentioned Ahiru Store, I'm going to presume you are looking for a casual wine bar or somewhere with a friendly bistrot feel. Because of the recent wine bar boom, and it's (over)exposure in various food magazines, such as Dancyu & Shokuraku, Ahiru Store is almost impossible to get into - even on a week night. You can make a reservation between 5 and 6:30pm, or you could just try your luck if you want to go later - be warned, it's a long wait in the cold. Nearby is Cristiano's, which is a bustling Portuguese tapas bar.
This place has also gotten a lot of press recently, but bigger capacity, brisk service and later opening hours (until 3am), mean that it is relatively easy to get a seat without reservations. But then again, weekends will be more difficult, so please stipulate when you intend to dine.
Please provide more specific information so that people are better able to advise you.
Yes, I'm sure that 2 years ago you would have been fine. However, in the last year Ahiru Store has had a huge amount of publicity, most notably the cover and a 4 page spread in Brutus magazine's wine bar issue, which boosted its popularity and inflated its tabelog ranking. Friends recently endured a 90 minute wait for a standing table on a Thursday night. Best to go early at the start of the week... or else wait until the hype dies down.
Personally, I like Potsura-Potsura, in Shinsen. They specialise in Japanese wine and have an incredibly comprehensive list of varieties. The food is fantastic, the staff are friendly and well informed.