>>26745834In Alchemy, the Seven Primary Metals are influenced by the seven planetary influences. These being:
Gold (Sun)
Silver (Moon)
Copper (Venus)
Iron (Mars)
Tin (Jupiter)
Mercury (Mercury)
Lead (Saturn)
Gold represents willpower, vitality, energy, and success. The Sun corresponds to the heart (HeartGold) and distribution of heat in the body. Large portions of this can be related to Solgaleo.
The Moon is symbolic of water, psychic phenomenom, and collective consciousness (A lot of this fits Lugia's model).
Venus influences herbalism, arts like music and poetry, harmony, proportion, integration, opposites into a whole (Zygarde red and blue cores combining, possibly?). This could either hint to Zygarde's role as a guardian of an island or even another unreleased Pokemon (such as Gigareki, maybe?).
Iron acts in conjunction to frequently violent energy. It is said in alchemy to increase psychic ability and to bring emotional power to the physical realm. Mars corresponds to the muscular system, blood formation (which, according to one post on this board, is relevant to Koko being Hawaiian for Blood), and the purging of the body for health maintenance. This could easily relate to Marshadow, hence the inclusion of "Mars" in the name.
There are seven major operations of transformation in alchemy.
Calcination is the first, being to heat a chemical in a crucible to reduce it to ash. This is to make space for a new substance, as it is important in alchemy to transform a substance into an equal value (give a lot to get a lot). The heated chemical becomes a black mess, or a "black stage", a ghost of its former self. This may be related to Lunala, as it would explain its Ghost typing.
I would write more but there's already way too much here. I'll leave sources for others to read into more for links to possible SuMo lore:
https://www.youtube.com/watch?v=DGyYIJpMC-khttp://ordosacerdotalvstempli.net/seven.html 
