- Main article: Jasper
Jasper is a Quartz-type Gem created on Earth in the Beta Kindergarten about halfway through the Rebellion. Despite the poor conditions of the Beta Kindergarten, she, unlike the other Gems created, came out an "ultimate quartz" with the natural abilities to be a soldier. She was originally created for Pink Diamond, but due to her demise at the hands of Rose Quartz, Jasper was reassigned to Yellow Diamond. She fought in the Rebellion on Earth against the Crystal Gems. Despite her hatred for Rose, she respected her leadership and tactics. Thousands of years later, she is assigned by Yellow Diamond to be Peridot's escort to Earth while the latter checks on the Cluster and its prototypes. Jasper willingly accepts, in the hope that she will have the opportunity to destroy Rose and the remnants of her army.
In "The Return", Jasper arrives on Earth with the mission of being Peridot's escort, assigned by Yellow Diamond, while she checks progress on the Cluster. Upon observing the Crystal Gems, Jasper believes that they are a waste of her time and then ponders where Rose Quartz is because she was looking forward to fighting her. Jasper proceeds to insult each of the Crystal Gems and tells Peridot to blast them with the ship. To Jasper's surprise, the Crystal Gems survive the explosion thanks to Steven's shield. Jasper immediately recognizes the symbol on the shield being Rose Quartz's. She asks Steven, thinking he is Rose, why he took the form of a human boy.
In response, Lapis Lazuli begs Jasper not to hurt him, which prompts Jasper to become enraged at Lapis for withholding information from her. Jasper then disregards the mission and wants to show Yellow Diamond what has become of "Rose". Garnet attacks Jasper, but Jasper summons her Crash Helmet, deflecting her punch. She then causes Garnet to unfuse and poof, using her Gem Destabilizer. She lifts up Steven by his shirt, still thinking that he is Rose, and mocks him, explaining how the Crystal Gems are weak and that Rose has failed. She headbutts Steven and places him, the other Crystal Gems, and Lapis, in jail cells on the Gem Warship.
In "Jail Break", while on the Gem Warship, Jasper tells Peridot that they are going back to Homeworld with the captured Crystal Gems and Lapis. Peridot disagrees, explaining to Jasper that the whole point of coming to Earth was to check progress on the Cluster. Jasper, once again, disregards the mission and tells Peridot that delivering Rose Quartz (Steven) to Yellow Diamond takes priority. Later, Jasper discovers that one of the imprisoned Gems is missing from her cell and finds Garnet in the center of the ship. Jasper is annoyed that Ruby and Sapphire are fused again, and she explains to Garnet that "fusion is just a cheap tactic to make weak Gems stronger".
Garnet and Jasper begin fighting; Garnet dodges Jasper's attacks and breaks her destabilizer. Jasper then spin-dives at Garnet and causes both of them to fall through the deck and into the ship's engine room. While Garnet sings, she continues to fight with Jasper, once again dodging many of Jasper's attacks. Finally Garnet catches Jasper and throws her into the ship's main power source, causing it to explode. After the ship crashes on the beach, Jasper crawls out of the ship debris, obviously injured, and explains to Garnet that she only won because she is a fusion. Jasper catches Lapis when she tries to fly away and asks her to fuse with her. Lapis agrees, and the two proceed to fuse into Malachite. However, Lapis uses chains made of water to tie down their fusion. Jasper struggles to escape, and Lapis drags them both to the bottom of the ocean.
In "Chille Tid", when Steven enters Malachite's Realm, it is revealed that Lapis has control of the fusion. Steven's presence, however, distracts Lapis, and Jasper momentarily takes control. Jasper appears exhausted, and when she notices Steven, she becomes enraged. She crawls towards him, repeating the word "you". When she becomes close, she tries to grab Steven. However, she is stopped by Lapis, who once again regains control.
In "Super Watermelon Island", the civilization of Watermelon Stevens on Mask Island attempt to sacrifice one of their numbers to Malachite to stop the earthquakes that troubled the island. Thanks to Steven's vision of the event, the Crystal Gems track her down, and fuse into Alexandrite to fight her. Lapis finally loses control of their fusion and Jasper takes over. She releases the chains that kept Malachite back and is ready to fight Alexandrite.
As Malachite, Jasper states, "You know, you're right. There really is something more to this fusion thing! It's not just a cheap trick. You've really shown me a whole new world of possibilities!" Malachite is eventually defeated and forcibly defused by the Gems, with the aid of the Watermelon Stevens. Shortly after the fight, a Cluster-related earthquake takes place, creating deep fissures in the ground. Due to Jasper being unconscious, her body slides down a crack. Pearl tries to catch Jasper, but she is too late to save her from falling.
In "Hit the Diamond", Yellow Diamond sends five Ruby soldiers, Eyeball, Doc, Army, Navy, and Leggy, to retrieve Jasper. It is revealed that she was considered the "leader" of the mission, much to Peridot's surprise. Peridot, unaware that her fellow Crystal Gems do not know Jasper's whereabouts, tells the Rubies that they know Jasper's location. Steven lies to the Rubies and tells them that Jasper is on Neptune.
In "Alone at Sea", Jasper follows Lapis while she is on a boat with Steven and Greg. Jasper makes multiple attempts to board the ship, such as pulling down and snapping the string off of the fishing rod while Lapis is fishing, and trying to force her way on, causing multiple loud bangs to be heard and making the ship's engine fail. Jasper finally climbs aboard via the anchor chain and expresses her joy at seeing Lapis again. When Jasper sees Steven, she called him Rose but a "dulled-down" version of her and thinks that he is working for Lapis.
Steven summons his shield to protect Lapis, but Jasper laughs it off and says that it should be the other way around since Lapis is much more powerful, as Jasper describes her to be a "monster". Eventually, Jasper aggressively hits Steven which flings him across the ship's deck. Jasper gets down on her knees and holds Lapis' hand, begging her to fuse with her again since Malachite was so powerful. Jasper acts manipulative, claiming that she changed, but Lapis rejects the offer. Steven sticks up for Lapis once more which causes Jasper to aggressively charge at him, but with quick reaction, Lapis shoots a water fist through the deck floor, hitting Jasper high into the air and far away to an unknown location.
In "Gem Hunt", Jasper follows two Corrupted Gems in the Great North. She poofs one of them off screen, and later appears in front of Steven and Connie when they are in the middle of fighting a Corrupted Gem. Jasper brutally injures the monster, throwing punches to the face and slamming her to the ground by her tail. Jasper manages to poof the monster by forcefully pulling her gemstone from her body. Steven, Connie, and Pearl (who later shows up) are shocked to see Jasper. Jasper teases Steven, saying "Rose, look what I got", revealing both of the monsters' gemstones. Jasper then walks away and disappears into the snowstorm.
In "Crack the Whip", Jasper rises out of the ocean on the beach with her two monsters. Before Jasper rose to the surface, Amethyst defeats one of the monsters that appeared first, and Steven bubbles her gem. Once Jasper is on the surface, she is seen on top of the other monster with her crash helmet equipped. Jasper reveals to Steven, Connie, and Amethyst that her plan is to create her own army to rival Rose's (Steven's). Amethyst tells Steven and Connie to go after the monster and that she'll take Jasper herself. Jasper is amused, but is also disappointed because she wanted to fight Steven, and not a "runt". Jasper then brutally knocks Amethyst on the ground and rolls over her helpless body with a spin dash. Jasper becomes bored, and wonders why Amethyst isn't trying her hardest. She says Amethyst is a Quartz soldier like her, but she's defective, and Jasper says she lives to fight. Amethyst tells Jasper that Rose said she was perfect the way she is. Jasper insults Rose by saying that she had low standards, causing Amethyst to become furious. She spin dashes at Jasper, but Jasper easily stops it and manages to poof her by slamming Amethyst to the ground with her helmet. Jasper holds Amethyst's gemstone in her hand and plans to shatter it.
When Steven and Connie see what Jasper is about to do, they charge at Jasper and fuse into Stevonnie. Jasper is surprised by the fusion, and after Lion launches the monster toward her, the monster tries to flee, but Jasper tugs her by the tail and mounts her. Stevonnie mounts Lion and Jasper is excited to face them head-on. The two charge at each other, on their respective mounts, and at the last second Stevonnie jumps into the air, throws a shield at Jasper, forcing her to catch it, and they poof the monster with Rose's Sword. Jasper takes the monster's gemstone and tells Stevonnie that she will be back and Jaspers always get what they want. She turns away and retreats into the ocean.
In "Beta", it is revealed that Jasper was created in the Beta Kindergarten halfway during the war when Homeworld needed to quickly grow more Quartz soldiers. She came out as the perfect Quartz, as described by Peridot. Later, Jasper is shown to have caged up a lot of Corrupted Gems behind metal bars from Injectors in the holes of the Beta Kindergarten.
In "Earthlings", Jasper talks to one of the Great North Monsters (who is caged up) about how she is a disgrace and an embarrassment to Homeworld along with being a pathetic Quartz. Amethyst attempts to sneak up on Jasper by walking across the edge of a cliff above her, but Jasper notices and Amethyst falls to the ground. Jasper wonders if she wants a rematch, and tells Amethyst that she was destined to lose to her the moment she came out wrong. Steven runs to Amethyst’s aid and explains to Jasper how that isn’t true, but Jasper claims that all Gems must serve the order of the Diamonds, and those who stray away from that objective must be punished. Jasper says that to come out wrong, to not serve the Diamonds, and to protect the Earth are disgraceful acts.
Amethyst swings her whip before Jasper can counterattack and ends up pushing her back twice, but does no damage. Jasper attacks Amethyst and she falls on the ground, but before another attack can be made, Steven launches his shield and causes an injector to fall, separating Jasper and Amethyst. Steven and Amethyst fuse into Smoky Quartz after Steven cheers her up, and Jasper angrily asks if fusion is the only trick the Crystal Gems can pull off. Jasper becomes enraged by Peridot’s laughter and attacks Smoky Quartz head on, but she easily counterattacks, even causing Jasper to slam into the cliff side and release some of the caged up monsters. Jasper notices that the Green Great North Monster is still caged up, and fuses with her. Smoky Quartz is still able to stop this corrupted fusion, and the Green Great North Monster flees following Jasper’s attempts to forcefully refuse with her.Jasper lies on the ground with inflamed arms and laughs off the fact that nobody she fuses with ever wants to stay.
Green spots began to form on Jasper’s body, along with spikes, to Peridot’s disgust, causing Smoky Quartz to unfuse when realizing it’s corruption. Steven tries to calm Jasper down in order to heal her. Jasper still sees him as the enemy, and says "Rose" out of breath. Steven explains that he is not Rose and just wants to heal Jasper. Steven licks his hand and reaches out to Jasper, which causes her to lash out and knock Steven backwards. Jasper tells Steven that she understands Rose’s methods now: she waits until after Gems are weak and useless and then manipulates them to join her team. Jasper points out how Peridot was stripped of everything, and Peridot explains how the Earth is not a bad place and that she is always learning new things, about the Earth and herself.
Jasper goes on to say, as her corruption worsens, “Earth… is a prison. And I got out because I’m better than this place. I only came back to finish you off. You can’t manipulate me Rose Quartz!... I’ve been fighting from the second I broke free from the Earth’s crust! Because of what YOU did to my colony, because of what YOU did to my planet, because of what YOU did to my Diamond!” Steven asks “Yellow Diamond?”, and to Jasper's dismay, she responds, “My Diamond... Your Diamond... PINK. DIAMOND!!” before becoming fully corrupted, revealing that Jasper and Rose both belonged to Pink Diamond at some point. Peridot launches a bar of metal through Jasper’s chest, poofing her, and Amethyst bubbles and sends her to the Temple.
Despite being corrupted, poofed and bubbled, Jasper left a lasting impact on the Crystal Gems. In "Back to the Moon", Amethyst pretended to be Jasper in order to deceive the Rubies, who had recently returned to Earth intent on retrieving her.
In "Kindergarten Kid", the Crystal Gems have to clean after Jasper's mess, releasing and taking care of the rest of the corrupted gems Jasper kept prisoner in the Beta Kindergarten.