This is for some my foreigner friends who might like to visit Japan...
1) What is like April in Japan?
It's like summer and winter lives in one months. But it's a nice trekking season, actually it is start of the trekking season. Cherry blossom starts in end of March to beginning of April, south to north... Every one is merry, some are drank from daytime... It does rain but not rainy season...
If you land Tokyo, most popular destination, the most popular hiking destination is Takao san. You can reach that by train(Chuo sen). You will be suprised that they have a beer garden at the top.
If you are a climber, you can go to Mt. Mitsutouge, and enjoy climbing with a great view of Mt. Fuji. Mitsutouge is known as an alpine training area...so you will see old pitons and rotten ring bolts... but climbing is easy. They have a nice hiking trail and you can also use trains.
Japanese Alps are still in snow... usually until 2nd week of April you can still ice climb.
For sports destination, Jyoyama is famous. They have chemical bolts.
Okutama mountain area is also good hiking destination and they have a lot of boulders.
Futagoyama is limb stone.
2) Kyusyu
I currently live in Kyusyu, the southern of Japan. Kyusyu is hot spring paradice!
So many Koreans and Chinese people visit Fukuoka, Oita, Kagoshima... etc.
Kyusyu is a popular holiday destination for Japanese too... I visited Ibusuki for sand soaking hot spa... and Mt. Kaimon dake.