Swallowtail

Wonderful butler café! No pictures allowed inside, but the butlers, decoration, and food do not disappoint. You have a small chance of walking in but you will almost certainly need a reservation.
I strongly recommend going with someone fluent in Japanese. The butlers will take your bags and coat from you when you enter; they’ll seat you (and also unseat and reseat you if you go to the restroom — and they escort you to the restroom so yeah, you’ll need to know enough Japanese to understand the instructions); pour your tea for you (you aren’t supposed to poor it yourself — ring the bell!). They do have an English menu so foreigners are welcome, though we were the only foreigners there.
The food was also delicious. I got the beef stew and dessert set. I recommend looking at the menu online (it changes each month) to see the pictures before hand. They also have afternoon tea (scones and sandwiches) and pasta. A lot of people just go for tea and dessert.
They have seats for one person, and for parties of two to four. They might have places for larger groups but I didn’t see them. The one person seats were really nice and private.
I will definitely go back if I can. It’s expensive though, the set I got was 3800 yen.