This train, Aso Boy! connects Kumamoto and Beppu via Aso. When you go to Mt. Aso by a train, take the Shinkansen to Kumamoto and transfer to this train. This is the easiest way to get there.
This train offers not only access to Aso but also a big fun, especially if you travel with child(ren). This train is operated by the refurbished Kiha-183 series. This was completely redesigned by JR Kyushu chief designer, Eiji Mitooka. The facilities of this train make both parents and children enjoy the ride to Aso.
You will find how nice this train is for kids in this article.
In spring season, the busiest period is late April and the beginning of May. It is called “Golden Week” in Japan. April 29, May 3, 4, and 5 are National holidays. If you can, lease try to avoid travelling on those days.
This itinerary includes many popular spots throughout Japan in 14 days. This itinerary starts from Tokyo. But if you want to start from Osaka, you can start from Day 11 to Day 14, and then start from Day 1 to Day10. Actually 14 days in not enough to see all popular spots in Japan. I include Hokkaido in this itinerary. But it does not include Shiretoko because of not enough time. I could not include south part of Kyushu, Hakone and Mt. Fuji either. If you can give up Tohoku part, you can get more time in Hokkaido. Of course you can go to Shiretoko.