Onion is a canon character in Steven Universe.
Onion is a fair-skinned boy with a small tuft of blonde hair and a chubby face. He wears a white sweater, a blue shirt tied around his neck, and red pants. His most recognizable trait is his onion-like head (although the top is thinner than the bottom, not resembling a normal onion). He also does not have any visible ears.
Onion is a very quiet kid who chooses not to speak to anyone except for his dad. When he speaks to his dad, it is in an unknown language. Onion is eager to help people. He will blindly follow orders even if they don't seem very well thought out, such as in the episode "Bubble Buddies", when he shot a harpoon at Steven's bubble. He cannot stand being lied to, especially by close friends. He has been seen to be bad as in "So Many Birthdays", he was seen stealing tickets from an arcade machine, which explains how he had enough to win a moped in "Arcade Mania". This is further emphasized in "Onion Trade" with Onion's delinquent behaviors such as destroying the moped for no apparent reason. Onion's delinquent behavior can be attributed to his severe loneliness, due to his father constantly being at sea. He does not seem to understand or simply not care when and if he is hurting people, has no qualms with stealing what he wants, and does things obliviously in the name of fun. This may be contributed to his young age and lack of moral understanding.
Steven is Onion's friend whom he is eager to help and has known him in the past. They may get along, but it is a one-sided relationship as Onion isn't known to talk to anyone but his father and his mother. However, his mother says that Onion talks a lot about Steven. Steven seems to wonder what Onion is doing most of the time. In "Onion Friend", Onion seems to do certain actions specifically to push Steven's buttons as a form of childish teasing, wasting food intentionally knowing that it bothered Steven and pretending to feed a mouse to his pet snake in order to scare him. He also seems to steal from Steven pretty often, from his Ranger Guy to his bag of chips. Onion, however, is shown to care about Steven as he gave him the Explorer Gal.
Onion doesn't see his father often, and this causes Onion to spend a lot of time wandering around, unsupervised. When Onion does see his father, he has been shown to speak to him in an unknown language. Yellowtail is one of the people Onion has been shown to speak to.
Vidalia, his mother, shows a very close relationship, with her being the only person he talks aloud to, albeit just the word "mama". She also encourages his expressive nature.
- Onion is seen behind Connie in the intro where Mr. Smiley stops him from running out into traffic.
- Onion only communicates to his parents, and when he does it is just random sounds.
- Steven doubts that Onion is a human, as seen in "Marble Madness".