Japan has four seasons.There is also in the anime season.
This video was made to focus on the season.
The story has a seasonal stream.spring,summer,autumn,winter...and spring comes back.
Each season features if you have, it appears to the activities and nature.
Also appearing in people's facial expressions, I think.
Watch this video want to pay attention to people living in "Four Seasons".

For editing :
Each one has a long scene. The clarity of the season by viewing the flowers and leaves and background .
Masking is not used, the effect can only several places. (To show the original anime.)