- Not to be confused with Sonia the Hedgehog.
Princess Sonia Acorn is the daughter of King Sonic and Queen Sally, and sister of Prince Manik Acorn. Sonia greatly resembles her mother, but inherits her father's super speed and eye color. She is princess of the Kingdom of Acorn.
25 Years Later (Unaltered)
In the unaltered timeline, Sonia is the daughter and first-born child of King Sonic and Queen Sally, and elder sister of Manik Acorn. She was shown to be fond of Tails upon his departure for Downunda, unsurprising given his history with her parents. Along with the rest of her family she came to Angel Island to visit the family of her best friend, Lara-Su. She and a group of other girls soon enjoyed a sleepover, which Manik of course intruded upon. (StH: #137, #138, #139)
25 Years Later (Altered)
Due to Sonic's travel to the past, Sonia was erased from the timeline, putting a mental toll on the former king. However, after Shadow's defeat, Sonic brought up the idea of kids to Sally... (StH: #166, #167)
Five Years Later...
Five years afterward, Sonia was yelling at her brother Manik to move so she can see the TV and herself on it. She complained when she learned that her parents were going out for the night, but quickly changed her mind when she found out Lara-Su was babysitting them. She later caused havoc with her brother Manik, forcing Lara-Su to use Chaos Control to rein them in. Lara-Su then put them to bed and read them a few bed time stories, which seemed to put them to sleep. However, the two soon sneaked out of their room and caused more trouble, resulting in a pillow fight with Lara-Su. The next day, they attended the celebration of the Five Years of Peace, when a missile was suddenly launched at the royal family. However, they were saved by the timely arrival of Silver the Hedgehog, who then explained to Sonic and Sally why he had come. Sonia then joined her mother, brother, and the unconscious Silver in fleeing to safety after the Dark Presence invaded the castle, though Sally had to carefully convince her strong-willed daughter not to go back and confront the intruders. She was later seen with her mother and brother in the Panic Room watching her father and a new group of Freedom Fighters re-take Castle Mobius. (SU: #5, #6, #7)
Water begins to flood into the Panic Room. Her father arrives before anything serious can happen. Doing as her father says, Sonia rode a rock as a surfboard, escaping the castle. The twins contribute to the efforts of the Future Freedom Fighters by reminding Sonic about his fight with Perfect Chaos and doing a spin dash with her brother after Sonic fails to hit the brain of Perfect Tikhaos. Sonia joins the team with her brother after the fight. (SU: #8)
The M:25YL Sonia is very mature and assertive, and has slightly more tolerance for her royal duties than her brother, which includes frustration, than Manik, who as first-born male, is heir to the throne of Mobius. Sonia was also best friends with Lara-Su, the daughter of Knuckles, once stating to her she "would hate to lose you as a friend."
The M:30YL version of Sonia is very fun loving due to being a child, and also gets annoyed with her brother easily. Despite this, the two both enjoy making trouble, especially with Lara-Su, whom both adore despite the near 20 year age gap between them. Sonia is also strong-willed and dislikes the idea of anyone invading her home. Given her mother's efforts to avoid using the words "panic room" to describe their safe destination, it seems that Sonia is also highly excitable.
- Sonia Acorn was named after Sonia the Hedgehog, Sonic's sister from the TV series Sonic Underground.
- It is unknown if Sonia could spin dash in the unaltered future as she has never shown that ability.