Summer in Japan is festival season. The days are hot and humid and the evenings are pretty much the same (except just a little less hot). It thus figures that the best time to hold an outdoor festival is in the evening when the temperature has dropped a little.
There are fireworks, traditional dancing, taiko drumming, stalls selling festival food and cold beer, and locals dressed in traditional costume. In some ways it reminds me of a Scottish Ceilidh (dinner dance), which provides the rare occasion for everyone to dress in kilts and dance the night away.
Of course wearing a kilt in the traditional manner at close to 60 ° North is quite a different climatic experience to wearing a Yukata on a balmy summer evening in Japan.