Sonia the Hedgehog is the sister of Manic the Hedgehog and Sonic the Hedgehog from the Sonic Underground reality. Despite being raised by an aristocrat and acting spoiled, she is an able Freedom Fighter, and helped Zonic the Zone Cop apprehend Evil Sonic after rescuing him from Robotnik's prison.
Before Giant Borg
Shortly after Sonic, Manic, and Sonia’s births, the Underground Zone’s local Dr. Robotnik would seize power of Mobotropolis and convert it into the polluted and metallic city of Robotropolis. A bounty was placed on the children of the queen, and thus Aleena was forced to take them into hiding. Eventually, the Oracle of Delphius appeared before her with a prophecy which foretold that she would have to separate with her children in order save they’re lives. She sent the siblings to three different caretakers, and Sonia was placed in the care of Lady Windimere, an aristocrat. As a result, she behaves in a rather spoiled manner. Sonia would learn how to play the keyboard and went off to form a band after meeting Sonic and Manic. The Oracle of Delphius reappeared to tell the children of they’re origins. Shortly afterwards, Dr. Robotnik captured Lady Windimere, as well as Sonic and Manic's guardians, and roboticized them. It was then that the three hedgehog children would form an alliance with each other to locate they’re missing mother. (SSS: #10)
Giant Borg's Attack
Sonia and her siblings would engage Robotnik in battle many times. Evil Sonic would appear in the Underground Zone on a mission from Robo-Robotnik to recover the Giant Borg. Believing Underground Sonic also possessed a piece of the Giant Borg; he located and interrogated him and his siblings. The evil hedgehog departed only for two new Sonics to appear: Prime Sonic and Zonic. Sonia, Underground Sonic and Manic mistook Prime Sonic for Evil Sonic until the two new hedgehogs explained who they are. Zonic would remark how he had a lack of data on Underground Sonic and the Sonic Underground dimension and would request an explanation of the Zone’s history. (SSS: #10)
Sonia, Manic and Underground Sonic would then team up with Sonic Prime and Zonic to stop the threat of Giant Borg. After defeating Giant Borg, Sonia and Manic freed Evil Sonic from jail after Robotnik imprisoned him. For helping Robotnik get the components of Giant Borg in the first place, Evil Sonic was then taken into custody by Zonic, who left Sonia and her siblings to continue their fight. (SSS: #10)
As she was raised with luxury and wealth, Sonia tends to be quite high maintenance, spoiled, and snotty. She hates getting dirty and constantly worries about the condition of her hair and clothes. Although she appears to be selfish, she is generally good-natured and helps those that are in need. Sonia is known to occasionally talk like a valley girl, despite being voiced by a male in the English variation of the show. Sonia always addresses her mother as simply "Mother", due to being raised in polite society.
Despite all this, Sonia has been shown to like performing daring acts, such as walking on a high brick wall. She is also very athletic, and appears to be good at gymnastics. Sonia is very self-sufficient and does not hesitate in taking on any threat or challenge that she may encounter, often coming out on top. She likes to think things through and on many occasions, has helped her brothers out of their own troubles (although she sometimes thinks of them as nothing more than pains).
Sonia is physically the strongest of her siblings. She is able to lift heavy objects as well as destroy barriers of various materials. She is skilled in martial arts, which she uses for offensive and defensive measures, and is also extremely agile. She does not have Sonic's speed, but is able to use the "Sonia Spin", where she spins around a horizontal (rather than vertical) axis (similar to the attacks eventually used by Blaze the Cat).
Sonia's medallion transforms into a Keyboard synthesizer which is capable of firing laser blasts as well as creating smoke screens. The keyboard also transforms into a laser rifle which she uses to attack.
Sonia wears a dress with a short dark purple skirt, and a red sleeveless top. The two sections are separated by a gold belt that forms a pointed shape at the front with a small circle in the center of the belt. Unlike most Sonic characters who wear gloves, hers are purple, and go up to the elbows rather than the stereotypical white hand gloves. Sonia also wears red stockings under dark purple boots, the toes of which are a matching red.
- When Sonic mentioned Princess Sally, Sonia made a face of disgust for unknown reasons. It is possible that Sonia was appalled at the idea of another Freedom Fighter princess, particularly one who was actually recognized as royalty while Sonia is usually just treated as a sibling by her brothers.
- A character closely resembling Sonia can be seen in Archie issue #134 during the scene when Sonic and Sally break up, sitting next to Espio the Chameleon.
- She is also the object of a crush from Robotnik's muscle henchman, Dingo, but she refuses his every advance. This is a rare instance, as Sonia was romantically involved with several characters in the series, including her universe's version of Knuckles the Echidna.
- Though the Underground version of Sonia is the only one to have appeared in the comics, Sonia does have a namesake in various alternate future realities. This character is a chipmunk named Sonia Acorn, and is named for Sonia while her brother Manik Acorn is named for Manik.
- Sonic Universe #50 was originally intended to feature a conclusion to Sonic Underground and thus Sonia's story. However, for unknown reasons, this story was delayed and appears to have been abandoned entirely.