I don't know why, but personally I think that "MOON" is about her dogs, especially Marron, who nearly died.
I know, the lyrics don't really fit and the dog in the PV is not Marron, but...I don't know...maybe it's just because I'm a strange person, but I think that in the PV Ayu describes the fear of losing somebody very dear and important to her, without being able to do anything about it (--> the black ink/liquid, which is holding her back).
And because Marron nearly died of cancer and Ayu was really helpless about it, this story came to my mind the first time I watched the PV!
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*i had a dream that you were gone*
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