In the myth-making that is Enoch literature (and to a lesser degree the book of Jubilees), the Watchers are angels sent by God to protect humanity. However, many Watchers fall because they lust after and cohabit with human women. Their offspring were known as the Nephilim, supposedly gigantic figures. Moreover, the Watchers give humanity illicit technological knowledge (weaponry, medicine, astrology). The Watchers who rebel are finally bound up by God, leaving 10% free to misguide non-Jews.
It is unclear if Rebecca Sugar’s Steven Universe draws upon this mythos, but there are certainly parallels. The Gems are extra-terrestrials vastly more powerful (in terms of technology and powers) than humans. In this case, the Gems are roughly equivalent to angels, with the Diamond Authority (Diamond, Blue Diamond, Red/Pink Diamond, Yellow Diamond)  as functionally equivalent to deities. In Message Received, Peridot describes the Diamonds as flawless, fitting with their namesake (diamonds are virtually indestructible and can only be destroyed by other diamonds).
However, SU flips the script on the Watchers mythos. The Gems are malevolent from the perspective of earth, whose empire is meant to colonize other planets and eradicating the organic life in the process. Until this point, the Crystal Gems’ rebellion has largely been unexplained, but presumably Rose Quartz as the leader wanted to protect the organic life on earth. The Watchers script is flipped: it is not the Godlike Diamond Authority who are good, but rather the rebellion itself is good. Rebellion far from being a bad thing as it is in Enoch literature is portrayed as integral to the existence of organic life on earth. The abrogation of the rigid Gem hierarchy is what leads to the development of human civilization on earth (similar to the Watcher’s mythos in Enoch literature).
Rose Quartz even has parallels with Watchers in that she falls in love with a human, leading to the birth of Steven. This script is flipped as well: a figure read as a woman falls in love with a human male, the inverse of the Watchers mythos. Moreover, the script is flipped because in Enoch literature, the copulation between angels and human women seems to be the product of lust not love.
Again, it is unclear whether the parallels (and inversion of discourse) between Steven Universe and Enoch literature is intentional. However, the inversion of the discourse produces interesting results. SU does not envision the social hierarchy of the Gems as good. Enoch literature like various literary text of the Hebrew Bible, envisions hierarchies as good. Abrogation of this hierarchy resists imperialist (the Rebellion, and Rose Quartz’ leading the rebellion against the view that organic life on earth is inferior and thus worthy of obliteration), racist (Pearl’s participation in the Rebellion, who are supposed to be “servants”), and queer antagonistic discourses (Garnet’s participation in the Rebellion). I am interested to see where Steven Universe goes with what precisely happened during the Rebellion.
 Though in later literature, the Nephilim are described as giants, they are only giants in Numbers 13:33. Read synchronically, the Anakites described as Nephilim in Numbers are also giants in Deut 1:28 as well as the Emim. There, they are not described as Nephilim, but rather Rephaim. The account of the Nephalim in Gen 6:4 does not mention the Nephilim being giants, but only the heroes of old (המה הגברים אשר מעולם אנשי השם ‘they were the valiant men from old, men of renown’).
 It’s ambiguous whether it is a Pink or Red Diamond. Interestingly, Pink/Red Diamond appears only in some of the art that we find in various Gem locals. My speculation at this point is that Rose Quartz and Pearl were part of Pink/Red Diamond’s group. Pink/Red Diamond perhaps supported or even launched the Rebellion against colonization of earth leading to her destruction by the other Diamonds (hence why her motif is lacking in other Gem locales).
 It is still unclear why Pearl decided to join Rose Quartz. It is also not exactly clear with Garnet either, although reading into “Steven’s Birthday” it seems that Ruby’s accidental fusion with Sapphire was abhorrent to the rigid hierarchical system of the gems (Sapphire is aristocratic while Ruby was a “common soldier”). The love between the two Gems and their fusion seems to be the reason for their joining the Rebellion. Amethyst emerged from the Kindergarten after the end of the Rebellion, and protects Earth because it is her home. Peridot joins the Crystal Gems because she believes that Earth has unique