Sunstonnie has a fire-shaped head with a long flair kept in a ponytail, bright orange skin with normal orange patches, and two sets of arms: one bulky and muscular with the other slender. The smaller pair can often be seen displaying peace signs or shakas, demonstrating their laid-back nature.
They wear a pair of dark red shades, covering their eyes, Steven's t-shirt with the sleeves rolled up, Garnet's gloves at the lower arms, and Steven's pants as shorts with a red pocket on the left leg and a blue pocket on the right leg,
Sunstonnie displays a combination of Garnet's leadership, protective spirit, and effortless natural cool, mixed with Steven's sunny optimism and tendency for sentimentality, and Connie's focus and compassion, all of which combine into a being of earnest, almost cheesy positivity. In many ways, they resemble a 1980/90s after-school-special cartoon character; offering self-esteem-boosting platitudes and giving helpful advice to children. Overall, they have a hip, laid-back personality even in the heat of battle. Much like Sardonyx, they like to break the fourth wall, encouraging the kids at home not to fight when it can be avoided.
They also have an limitless compassion towards others, even towards those that others would think deserve what they've gotten, such as with Spinel.
Sunstonnie first appears during the rematch fight between Stevonnie and Grogar on Earth during the giant Gem Injector incident. After getting itself known to the team, their first action was saving The Diamond Authority from getting crushed underneath the Gem Injector. They then save Spinel from falling to her death within one of the cracks of earth created by the Gem Injector, telling her that no one deserves to get hurt or bullied. After that, they try to climb the Gem Injector to try and stop it, but they were stopped half way by Grogar using the Rejuvenator on them, splitting them in one slice.
- The original concept for their appearance was to have just Sunstone appear, but Sunstonnie was created instead as Stevonnie was involved in the fight with Grogar.