As a newcomer to your story, who are the main cast of characters that I should be familiar with? I know the mc is a Hematite, but I'm not familiar with the rest
Also might be a silly question, but you've mentioned the Diamonds in the past. Are these the same Diamonds as the canon ones from SU, or are they new, original versions exclusive to the Harvester?
We'll address the second part of the question first since it's shorter! [and no question is silly! We love any asks we get out of genuine curiosity :3]
They are NOT the same versions as Steven Universe's canon! They are completely original versions, and were designed based on the statues in the Sky Arena of SU.
TL;DR on the bios [taken straight from @gemsontherocks ]: White is the mysterious, stand-offish scientist. Yellow is the militant and workaholic inventor. Blue is easy-going and doesn't seem to take her Diamond duties seriously.
Yellow is the 'closest' to Canon SU's Diamonds, but don't let her appearance fool you, underneath that familiar exterior is a VASTLY different gem than SU Yellow.
Actually I take it back, Pink is the closest to SU, but even she has some key differences!
NOW for the first part! [Since this post will already be large, no references in the replies FOR NOW, but rest assured character bios pages are in the future.~]
It's a big cast of characters, but it's drip-fed through the arcs and doesn't bombard you all at once!
Obviously you have the Diamonds above, and you know of Hema already, but the story is somewhat divided into three 'groups' of characters. These groups interact frequently, but have clear divisions that make them feel like sub-casts. [But if a gem intersects enough with two groups that they could be counted in both, I'm putting them in both!
You have the "Diamond Prism" gems
You have the "Hematite Kindergarten" gems
And then you have "The Civilians".
[There's technically a fourth group but they're not on Homeworld and won't show up until arc 10-11 so we're leaving them a surprise]
The Diamond Prism Main Characters: Hema, Red the Pink Pearl [Arc 5], White Diamond, Yellow Diamond, Blue Diamond
The Diamond Prism Secondary Characters: Rubes the Ruby [new addition], Morganite, Frecks the Peridot, Hacker the Hackmanite, General Topaz, White Pearl, Yellow Pearl, Blue Pearl
The Hematite Kindergarten Main Characters: Hemmi [Hematite 2], Tam [Hematite 4], Mite [Hematite 5], Meta [Hematite 6] [old model below], Mati [Hematite 7], Mago [Hematite 9], Hita [Hematite 10], Ti [Hematite 14], Tiny [Hematite 15], Kyan the Kyanite, Morganite, Frecks the Peridot, + 2 Redacted characters
The Hematite Kindergarten Secondary Characters: Big Guy [Hematite 1], Tita [Hematite 2], Tae [Hematite 8], Spike [Hematite 12], HT [Hematite 13]
The Civilians Main Characters: Morganite, Eka the Ekanite, Sphal the Sphalerite, Frecks the Peridot, Hacker the Hackmanite [incomplete]
The Civilians Secondary Characters: Rubes the Ruby, Puff the Jasper [incomplete]
Cast Size Chart [with some members missing! This chart is incomplete]
From left to right: General Topaz, Morganite, Blue Diamond, [newling Hema behind BD], Yellow Diamond, Hema, White Diamond [old model], Red the Pink Pearl, Eka the Ekanite, Sphal the Sphalerite, Hita, [Big Guy in the background], Tiny, Hacker the Hackmanite, Mati, Frecks the Peridot, Meta, Mago, Kyan the Kyanite, Tam, Mite, Ti
Since there's so many characters, and to tell you about all of them would make this far too bloated and would ruin some of the magic of experiencing the story as a new reader, for the time being, have their character designs and make up your own assumptions about them! Always a fun game before you properly meet them in the story.~