In Japan, everything starts in April.
Traditionally, companies starts their fiscal years from April, and schools starts new grades and classes from April. Moreover, a lot of things like marriage, traveling, moving, studying or diet are talked about in this season.
There are some reasons why Japan starts all the things in April, not in September.
I said some, but it's actually 3.

1. Because There's April Fool Day.

Google Map April Fool 2013
Google Map on April Fool 2013
April Fool, the 1st of April is the day you can make fun of anything. As the jokes gets worse and worse these years. people can forget the seriousnes and nervousness that you start a new thing.
In addition, you can declare anything big on April Fool, and call it off after you find it difficult.
There has to be a room for an excuse.

2. Because It's After March.

Marching Band
After something great or something marching, you tend to do something new.
Not too slabby, if i do say so myself.

3. Because It's Spring And Cherry Blossom Season.

Cherry Blossoms
Nothing can't be more reasonable.
In any year in any place in Japan, people love to see the cherry blossoms blooming and feel like being fresh, feel like starting something.
Cherry blossom, Sakura, is not only as a milestone of changing seasons but a begining definitely.
The season is closing as the petals are flying away now.
If you missed it this year, don't forgrt to come and enjoy it in Japan next April.