Not gonna lie, that Akashic Record reference? That is awesome.
Those that do not know, Devil Survivor 2.
That's the only hint you're getting.
Dreok Crushedthroat (Guest)
Now we just need the Root, the spirits of 7 Heroic Gems, Steven to dye his hair orange, and the tone to get darker.
Incidentally, Pearl as Lancer would be amusing.
Fire Flyer (Guest)
Hmm... Okay, in a hypothetical Grail War composed of only Gems, we'd probably have...:
Saber - Rose? Maybe? She's got the sword. (Or possibly Connie, if we're counting non-gem characters
Lancer - Pearl (no contest)
Caster - Lapis Lazuli due to heavy use of aquakinesis/Peridot ("sufficiently advanced technology is indistinguishable from magic")
Berserker - Sugilite, because Sugilite
Assassin - ...Not sure about this one. Garnet, maybe? She seems like the only one outside of Pearl who knows how to sneak.
Archer - Opal, due to her being the only one with a bow
And for some irregular classes...
Avenger - Jasper; she's got the anger issues for it
Shielder - Steven, no contest
Beast - The Cluster, probably.
Wooooooooo! Grinder Golem combo let's gooooooo!!!! /jk
Next page will be Monday.
I figured Reflectory of Akashic sounded cooler and more fanciful than just 'the weird gem mirror that supposedly knows all' because it has a gem trapped inside'. Akashic being a reference to the concept of the Akashic Record which if you know about it, good for you!
And if you don't, at its simplest it's just like the library of all knowledge and history since forever.