When a prison holds the sun inside it, everything will always be in season. Obviously if the sun is in prison, the seasons can't change. Want to eat perfect apples all year round? Just put the sun in prison when they're ripe — usually a short window of ten days.

When things are in season for more than ten days, people are going to wonder what's going on. When's Christmas? When's Golden Week? Soon (しゅん), you say. Soon enough, it's June (じゅん). Which is the middle of the year, so now everything is soon.