The "Watermelon Stevens" are characters who appear in "Watermelon Steven", and are the episode's main antagonists. They reappear once again in "Super Watermelon Island".
The Watermelon Stevens are all Steven-shaped humanoid watermelons. They have bumps on their heads resembling Steven's hair and are close to Steven's height. They each have two black seeds for eyes and dark and medium green stripes running vertically down their bodies.
The Watermelon Stevens were brought to life by Steven, who, without knowing he inherited Rose Quartz's phytokinesis ability, started spitting watermelon seeds outside of It's A Wash. Steven's saliva caused the discarded seeds to develop into fully-formed sentient watermelons by the next day.
Rose's plants acted as her guardians, and similarly the Watermelon Stevens defend Steven from harm. Though initially docile, the Watermelon Stevens become increasingly aggressive towards any possible "threats" to Steven, regardless of Steven's commands and/or the lack of any real danger.
In the time between "Watermelon Steven" and "Super Watermelon Island", the Watermelon Stevens have created a fully-functional society on Mask Island. In addition, they appear to have developed their own independent personalities.
After their formation, the Watermelon Stevens initially appeared to be inanimate. Steven takes a liking to one of the smaller looking melons, calling it Baby Melon. Steven displayed them in Beach City Funland intending to give them away, but Sadie insists on paying five dollars for one and Ronaldo draws attention to the sale, resulting in Steven selling all his Watermelon Stevens, except for Baby Melon which was not for sale.
Onion steals Baby Melon for himself, and as Steven gives chase Baby Melon suddenly moves, escaping Onion and reuniting with Steven. Realizing that all the other Watermelon Stevens must be alive, Steven recalls them, refunding his customers and taking back the Watermelons, who follow him. Ronaldo refuses to return a Watermelon and hits Steven with a spatula, which provokes an aggressive response from the Watermelons, who all start punching and kicking Ronaldo.
Steven returns to the Beach House to inform the other gems of the crisis. The gems accidentally provoke the Watermelons by pushing Steven back inside the house, and they fight. The gems destroy many Watermelons before the Watermelons hold them down by sheer numbers. Some Watermelons dig a hole in the ground for Amethyst, intending to mercilessly bury her with a bouquet of flowers.
Due to his lack of control over this new power, Steven cannot prevent the Watermelons Stevens' rampage. This inspires Baby Melon to sacrifice himself by punching Steven, diverting the Watermelon Stevens' attention away from the Crystal Gems, whom they were previously attacking. Upset, Steven tells them to go and not come back until they understand Baby Melon's sacrifice, and they comply. They were last seen walking deep into the ocean or along the beach, with some getting picked up by seagulls.
"Super Watermelon Island"
After the events of "Watermelon Steven", the Watermelon Stevens traveled through the ocean to Mask Island and colonized it. A civilization among the Watermelon Stevens was established; farmers grew more Watermelon Stevens and had them delivered to families during infancy. Some of the watermelons wear accessories, such as grass skirts, flower necklaces, and colored leaves fashioned into ties. New species of watermelon can be seen such as dogs, chickens, and horses.
In the center of a village, an elderly Watermelon Steven stands in front of a huge statue of Baby Melon with his arms out to the sides, the exact pose Baby Melon made before being killed. A group of baby Watermelon Stevens stand around the statue and a gong rings. Everyone in the village quits what they are doing and the statue is soon surrounded by Watermelon Stevens who all shut their eyes and put their index finger on their nose to decide which Watermelon Steven was to act as a sacrifice.
As Steven (in the form of a Watermelon Steven) is in the middle of this event, he is confused and does not put his finger on his nose, resulting in him being unknowingly chosen as the sacrifice. The other Watermelon Stevens draw a yellow star on his chest, put roses on his head, and place him in a chair, carrying him up to a cliff. At the edge of the cliff, Steven looks back at the watermelons who use body language to tell Steven to raise his arms in the pose of Baby Melon. He proceeds to, and Malachite rises out of the ocean. Malachite recognizes Steven and attacks him, causing him to wake up and inform the other Crystal Gems of these new events.
As Malachite continues her rampage the Watermelon Stevens flee into a cave. Steven possesses another Watermelon Steven and observes Alexandrite fighting Malachite, though the latter gains the upper hand. He enters the cave and gives a speech to the Watermelons, rallying them to fight Malachite. They attack Malachite (who is crushing Alexandrite) with bows and arrows, spears and shields, catapults, wing gliders and their bare hands. Though they deal no damage to Malachite, who destroys some of the Watermelons, they do distract her from Alexandrite, allowing Malachite to be defeated.
Steven reveals himself to the Crystal Gems, who thank him and the Watermelons for their support. The Cluster causes an earthquake, and the gems reassure Steven as he returns to his own body to take the drill to destroy the Cluster.
On Mask Island, the Watermelon Stevens created derivatives of their species:
A watermelon dog, also known as the Melon Mutt, travels with Steven. The dog brings Steven to the village and stays by his side throughout his time on the island.
Watermelon horses are used as transportation via horse and carriage to deliver baby Watermelon Stevens to families.
Outside of a family's home, three watermelon chickens can be seen. Due to the lack of any limbs, they are only able to rock back and forth. They taste like watermelon to a human, but they taste like chicken to the Watermelon Stevens.
In "Watermelon Steven", the Watermelon Stevens protect Steven when he is faced with any potential danger. In "Super Watermelon Island", Steven possesses a Watermelon Steven in his sleep. The other Watermelon Stevens do not appear to notice any difference in Steven's Watermelon, but they pick him to be a sacrifice for Malachite. When Steven possesses another Watermelon, a few other Watermelon Stevens notice. Later, Steven rallies the Watermelon Stevens to fight against Malachite.
Ronaldo buys a Watermelon Steven and decides to live-stream an autopsy of it for the website Weirdstar. Realizing that they are alive, Steven tries to stop Ronaldo and is hit with a spatula. This causes the Watermelon Stevens to react and attack Ronaldo.
Baby Melon saves Steven and the Gems from the other Watermelon Stevens by sacrificing itself. It strikes Steven, sending the wrath of the other "Watermelon Stevens" upon itself. As seen in "Super Watermelon Island", the Watermelon Stevens appear to worship Baby Melon as a sort of savior, having a statue of it in the middle of their village and mimicking the pose he made before his demise.
During "Super Watermelon Island", Steven, possessing one of the Watermelon Stevens, comes face-to-face with Malachite. Malachite recognizes the Watermelon as Steven and attacks it, most likely driven by Jasper's hate of Steven. It may be that the Watermelon Stevens sacrifice each other to survive and calm down Malachite. The other Watermelons hide from Malachite out of fear, but Steven (as another Watermelon) rallies them to fight her.
- It seems the Watermelon Stevens have no mercy, since they held down Amethyst and started digging a hole to dump her in. They may have even filled the hole back in with her still in it. The only mercy that was shown was when they got some flowers for Amethyst when they were about to bury her, which she comments are lovely.
- This changes in "Super Watermelon Island" where they have developed their own society as well as personalities of their own.
- Despite the fact that watermelons float, the Watermelon Stevens sink.
- When Watermelon Stevens are destroyed, they explode into chunks and slices of cut watermelon.
- Their life span is around 14 days.
- They are similar to Pikmin, from a game with the same name.