Fandom Specific Plot / Steven Universe

• The idea of Humanity Ensuing on the gems garnered Fanon popularity early on. More often or not, these Human AUs are specifically a College or High School AU doubling as host for High-School Sweethearts. Such fanworks have been acknowledged in promotional art on Twitter by Crewniverse members Hilary Florido, Jesse Zuke, and even the head girl herself.
• Early on, there was "Lapis Lazuli joins the Crystal Gems." Peridot and Jasper may or may not follow. Funnily enough, the first of these characters to join ended up being Peridot at the end of season two, after mouthing off to her superior. In canon, Lapis is adamant about not joining the group in any capacity, at least until the end of the original series, where she helps fight the Diamonds. Meanwhile, Jasper never joins, and doesn't even begin respecting Steven until the end of Future.
• The "Momswap" AU, in which Jasper, Lapis, and Peridot are the Crystal Gems and raise Steven. The canonical Crystal Gems take the place of the original Homeworld Gems to varying degrees, though this doesn't always happen. Sometimes Connie and Steven also swap roles, in which case Yellow Diamond usually becomes her mother, with Rose Quartz becoming Pink Diamond. ^note This turned out to be Hilarious in Hindsight following the reveal that Rose really was Pink Diamond.
• In general, a lot of fics utilize Peridot, Jasper, and Lapis as a sort of "Homeworld Trio," either as a secondary group of protagonists or a team of Psycho Rangers. In-show, despite even appearing together in the extended opening, the three only interacted as a group for maybe two scenes in a single 11-minute episode. In fact, with the exception of Lapis and Peridot (and even then, that took a while), they all explicitly dislike each other.
• The Permafusion AU, in which Ruby and Sapphire are defused and another of the team's Fusions (usually Opal) becomes the team's Permafusion.
• There are a good amount of fics that depict life just before Steven's birth, during his birth, and directly afterwards.
• There have been plenty of fics that depict what Steven's life would have been like if he had his mother in his life, including fics where Rose and Greg raised him together, Rose raising him as a single parent for one reason or another, or finding a way to resurrect Rose. The latter plot usually comes with a lot of drama for everyone, especially after the show revealed that she was Pink Diamond and all the baggage that entails.
• Gems cannot reproduce biologically, but that hasn't stopped fans from creating countless fanworks where Gems can lay eggs that result in baby Gems called "Gemlings".
• "Bad Pearl" is very popular in fanart. She's an Alternate Universe version of Pearl where she's a smoker wearing a leather jacket and jeans. She's pretty much the anti-Pearl— while Pearl is sweet, neurotic, and motherly, Bad Pearl is an overall bad influence, though she still has a good heart. "Bad Pearl" did eventually appear in one episode (she was created by a storyboard artist for the show so it wasn't an Ascended Meme), but she was just normal Pearl wearing a jacket and jeans.
• Right after the introduction of Blue Pearl and Yellow Pearl, many fanworks began discussing the way Homeworld treats Pearls. Some are even AUs where Blue Pearl joined the Crystal Gems, or where the Pearls on Homeworld start a new rebellion.
• Hurt Comfort Fics where Lapis either recovers from an abusive relationship with Jasper or Jasper recovers from an abusive relationship with Lapis. The one being the "comforter" is usually Peridot. In both cases, this type of fic is common in both canon complaint works and humanized works.
• With the reveal that Rose Quartz was actually Pink Diamond the entire time, there have been fics where characters learned the truth about her identity before she gave up her gem to have Steven.
• With The Movie's release, works about Spinel coming to Earth early are common, as well as AUs where she's been a part of the Crystal Gems since the beginning. Whether or not Pearl is still a member in these scenarios, or if the new CG!Spinel is aware of Pink being Rose, varies from fic to fic.
• After Future, time travel fics where certain circumstances leave a 16- or 17-year-old Steven Trapped in the Past (i.e., the original show during S1 or S2) started to be common. They tend to follow him trying not to alter the past too much, while still making sure this version of himself has a better life, and learning to cope with his trauma in a healthy way. A Tumblr blog that was one of the first to tackle this plot also popularized having future Steven use the alias "Twoie" and acting as Steven's older brother.
• Another popular plot following the end of Future are Crossover Fics where, during his post-series road trip, Steven ends up trapped in Gravity Falls due to the town's Weirdness Magnet properties and must temporarily work at the Mystery Shack along that show's cast as a result. Whether the story takes place during or after the events of Gravity Falls tends to vary, but the latter is more common.
• Back when the show's popularity first exploded, if a fanwork featured Steven and Connie as adults with children, at least one of the Fan-Created Offspring was guaranteed to be named in honor of Rose or at the very least look like her. The trend died off after the character became a Broken Pedestal for both Steven and the audience.
• The Diamond Swap AU, where the Diamonds' personalities and roles are swapped. It tends to play out almost exactly the same like in canon, even down to whoever assumes Pink Diamond's role becoming Steven's mother.