Thanks for breaking it down like that, it's interesting stuff.
So technically it's heart the organ, gotcha. Still, we're dealing with mysticism here and combining it with astrological alchemy, so you could probably still argue it's a heart in the spiritual sense like you say. And considering its golden counterpart is the brain which you could match with the Psychic type much easier I do think it makes sense to look at the heart in that way too. (You could probably also try and link HeartGold and SoulSilver to this stuff somehow.
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And I did notice that the location of Lunala's aforementioned "silver" bones match up with where the heart would be, guarding it like a ribcage. Notice the bright circle around that area in the purple? It does draw some attention to it. Another case of dualism?
Finally there's the whole cosmic theme, with the celestial bodies of course but also the starry domes on their heads, that one could use the explain the Psychic type. That's probably the most straightforward way to go. Cosmic Power is a Psychic type move for example.
Haha, yeah. Gen 7 echoes Gen 2 like Gen 6 did with Gen 1 confirmed?
Very nice, I'll give that a watch right away.
edit: also the speculation thread probably makes more sense for this stuff whoops
edit 2: watched it, very neat legend. now we only need to find a hawaiian bat legend