I lived in SE Asia for many years, it is also very hot there, we were right on the equator. But the AC was very cold in every place, and the cities were often designed to allow moving about the town without ever going outside (lots of underground tunnels with AC, for example).
Temperatures around 30C and locally over 33-35C may sound mild, depending on where you're from, but this is a country where summer temperatures usually hover around 20-25C. We're simply not used to it, and our houses are built to keep in the warmth, not get rid of it.
While summer is humid and hot in Japan I can't recall ever being this hot.