A theme of Pagoda of the Heavenly Mirror, the last stage of the Brilliant Route.
It's calm, yet majestic. Sets up the mood for the final confrontation very well.
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The soundtrack comes from "Brilliant Pagoda or Haze Castle", 4th part of Len'en series created by Trick Nostalgie. The game is available for free here: http://www.freem.ne.jp/win/game/13429
Trick Nostalgie homepage: http://mugentrick.tubakurame.com/
The soundtrack has been extended to play for 10 minutes.