I guess, the duality of the concept is more meant like the soft, positive side (happy, cheerful, loving) and the strong , negative side (aggressive, decided).
To sum it up (quoting myself):
The theme is Two-sidedness or Duality
Two overlapping sides of me become one.
W FACE ~inside~ contains songs from ballads to light pop songs, the emotional side. W FACE ~outside~ contains a variation of sounds, from dance tracks to Hip Hop/R&B and also one ballad sung with a simple piano - the aggressive side.