The 9th song from the album "Unbalance+Balance" by Akina Nakamori. What's interesting about this song is that Nakamori came up with the idea to write two songs with the same melody for the album. The 1st ended up being Eien no Tobira and the 2nd was Kagerou. Eien no Tobira was written by Natsuno Serino and Kagerou by Nakamori herself. Kagerou and Eien no Tobira definitely have different moods to them and the variations in the instruments used in the songs convey quite different, although similarly melancholic moods.

Eien no Tobira:    • 中森明菜 - 永遠の扉 | Akina Nakamori - Eien n...