It is important to check the Japanese calender when you plan on visiting. Huge portions of the Japanese public travels within Japan during holiday(s) so you may want to avoid these crowds (or worse, tickets to travel may be sold out). During Golden Week, which is the end of April to early May, schools and companies are closed due to holidays which as lined up as a block on calenders. Some holidays are variable depending on the year so if you plan on visiting Japan in 2015 or 2016, go check the calender for that year!