public static string ToJaCal(this DateTime d)
{
JapaneseCalendar jaCal = new JapaneseCalendar();
var nengo = new string[]{ "明治", "大正", "昭和", "平成" };
var nen = nengo[jaCal.GetEra(d) - 1] + jaCal.GetYear(d) + "年";
var tsuki = d.Month + "月";
var hi = d.Day + "日";
return nen + tsuki + hi;
}