stupidity and malice tend to the enjoined.
If and when I do visit Japan to see the husband's cousin, I will opt not to visit during both allergy seasons. Or I may end up clawing my own eyes out. As it stands, if I visit with my sister in tow, it will not be during summer. I might die of hypothermia.
On weather, my advice:- do not consider anything from early July through mid-September- avoid mid-June to mid-July as it rains and is humid, if not so hot as 'summer'- avoid December through February unless you exclusively stay in western-style, insulated, hotels- even then, you'll need to wear woolens for the freezing temples, etc.For allergies:- like me, you may have none on your first visit as flora species are a bit different- late-September grass seed allergies are nothing as bad as spring tree pollen allergies- that peaks in the second half of March through mid-April in TokyoThe best months then are:- late September through mid-November- late April through early JuneGood luck.