For the second year running I was in Tokyo in late August, and the Yona Yona popup beer garden was again in action in the Ark Hills shopping centre next to the InterContinental Tokyo ANA.
The pub opens up for a couple of hours at lunch, and then for the evening starting at around 5pm.
On one side of the bar there are half a dozen beers on tap, and a pint costs a reasonable ¥800.
On the other side of the bar you can purchase snacks that are enough for a meal. I had a rather decent chicken salad for lunch one afternoon, and the chicken was freshly cooked.
My choice of beer during my couple of days in Tokyo was a fairly decent porter called the Tokyo Black. I also had the namesake Yona Yona Ale (a pale ale) which was sometimes on special for ¥500.
In the evening the bar can be quite popular, but you should be able to get a seat as there are a decent number of tables and seats.