Sakurajima

When is the best time to see Sakurajima in Kagoshima Prefecture? Also, when is it the most active (volcanic activity, smoke)?

When ? Volcanoes unlike weather are difficult to forecast. You just have to do what I did. Include it in your trip and hope for a good day. We were unable to make the most of seeing Aso due to smoke...very toxic smoke.

I was able to visit sakurajima on a very good sunny day with my friend tour the place with rental bicycle and i got to vist an onsen which was a few minutes away from the ferry. however, when we passed by sakurajima the next morning, the whole island was covered with cloud. so i guess it requires some kind of luck.

Sakurajima is nice around the year. I suspect that the landscape is slightly less attractive during the winter month due to reduced vegetation.

As mentioned by Uji-san, Sakurajima is nice around the year but can be seen better when it is sunny and less windy. When it rains, mountain top is usually covered by the cloud. The mountain is a bit more active this year and we can see smoke almost every other day.