Onion is a minor character in Steven Universe and a resident of Beach City. He made his debut in "Laser Light Cannon" as a cameo character. As revealed in the episode, "Onion Friend", he is the son of Yellowtail and Vidalia and the half-brother of Sour Cream.
Onion is a very quiet kid who chooses not to speak to anyone except for his parents. But when he speaks, it's mainly in a foreign, gibberish language much like his father. Despite this, people seem to communicate just fine with him, showing no confusion whatsoever. 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, as shown in "Steven's Lion".
He has been seen to indulge in criminal activities, particularly thieving. In "So Many Birthdays", as he is 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. He also stole Steven's Chaaaaps and Ranger Guy in the episodes "Onion Friend " and "Onion Trade ", respectively. Onion's delinquent and kleptomaniacal behavior can be attributed to his severe loneliness as a grab for attention, 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 could be attributed to his young age and lack of moral understanding. He continues his bad acts in "Watermelon Steven", when he steals Steven's Baby Melon, despite Steven stating he wasn't for sale. In "Political Power", Onion seems to be on the verge of attacking Mayor Dewey as he held his baseball bat menacingly.
Later, in "Too Short to Ride", the severity of his criminal acts appear to have escalated. He is shown preparing to burn down the roller coaster at Funland when it had people on it, with implications that it wasn't his first attempt. In "Future Boy Zoltron", Onion is shown about to terrorize Funland Arcade with a crowbar. At this point Steven starts to worry that Onion will end up in prison.
He has also been shown to have a rather strange fixation with food, in that he is never seen eating it but instead throwing or destroying said food as said by Steven and proven in "Onion Trade" and "Onion Friend". The only food he does seem to enjoy is Guacola, as he is seen taking several sips in "Drop Beat Dad". He seems to have an overall strange personality, as he is a very difficult person to understand and predict.
Onion is a fair-skinned boy with a small tuft of blond hair and a chubby face. He wears a white sweater, a deep periwinkle shirt tied around his neck, and pale red footie 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.