I cannot say that summer is the best season to visit Japan. It’s very hot and very humid. But it’s vacation season anyway. School summer break kick off on July 20 in most of area. And mid August is called “Obon”. It is one of the busiest period in the year. If you travel in this period, train may be booked out quickly. Please see the details in the link below:
JR Group operate lots of seasonal trains during summer season. In this post, I show you many seasonal trains that will run in major tourist spots until the end of September.
*Autumn seasonal train schedule (October to November) will come up in late August. But you will find all schedules until February, 2018 for trains in Kyushu. Continue reading Schedule of 2017 summer seasonal trains of Japan Railways