Is OAK a place?
How is anyone supposed to answer this without you having said where you want to fly from?

People here will generally give as much time in writing answers as those asking invest in their questions.

To get you started, yes, there are better times of the year to go to certain parts of Japan than others. Summer can be unendurable for many people, the temperature might not appear to be so terrible but the humidity can be unbearable for those not used to it. I personally avoid Japan at this time of the year even though I usually enjoy hot weather having partly grown up in Spain.