What made SEASONS so big in Japan?

[Mimichild]

Interesting story! I was Skyping my friend who lives in Japan and she had the radio on and it played SEASONS. We stopped talking and began singing the lyrics then she was all nostalgic and said it brought back sad memories. So I wanted to know what was so special about this song because I felt that it wasn't one of Ayu's best ballads (average quality) but for others it maybe different.