the tldr is that this a battle about the equilibrium between gaia and alaya
it always seemed so important to me that is called the bleached EARTH phenomenon while the previous incident was the incineration of HUMANITY, it makes sense now that we know it was only the SURFACE of earth that was affected.
ok to start, i think is weird that our earth cannot create a proper archetype in PHH when it could in lb7. even in tsukihime, where gaia should be stronger, earth can only create arc thanks to the help of type moon. i think thats because of the creation of excalibur, the breath of the planet. anytime and her family go around the galaxy killing intelligent life, not planets or even non-intelligent life. we see that in lb6, even if it seems that theres no more landmass around, the earth and avalon are still fine and kicking, they are so fine in fact that avalon keeps sending shit to punish the veteran fairies, so technically there was no need for gaia to give away such a big part of herself to humanity, but gaia does love humanity and wanted to help them. so if arc is the "child" of gaia and type moon then excalibur is the child (or a contract) between gaia and humanity. arc does call excalibur a cousin but i think is more like a half sister and yes that means gaia is a slut. because gaia gave such an important weapon to humanity and that left her weaker, we know that at some point shes gonna call the types to make sure humanity dies alongside her. we know this is gonna happen in PHH because ort is also sleeping in there.