It a real production cel...
Its from episode 28, where the artist that is 
carrying one of the rainbow crystals, is 
explaining the story of some of her work.
(which looks like scenes of Endymion and Serenity 
in the moon Kindom)
"so thats why they call them illustrations of 
love" says Usagi.
I always interupted to be Usagi's vision as the 
artist is describing the story.