PERSONALITY
Sonechka is an untrusting, defensive, strange girl who treats everyone around her like an enemy. She's deeply paranoid, but rarely acts on these fears, preferring to sulk and complain to herself. She gets joy from the misfortune of others and is rarely sympathetic, often misusing her mysterious ability to predict the future to toy with or manipulate others.
Full bio here
VOICE
Sonechka's voice is nasally and congested. I've always imagined her voice being mid range, though I could see it going higher or lower as long as she has that nasally sound. She tends to speak intensely with a hint of resentment and anger at all times, only relaxing her voice if she wants to seem friendly but even then, I imagine those lines coming off as more sarcastic.
Sonechka also often quotes other people, usually using a mocking tone when doing so.
A voice reference would be Christine Cavanaugh's Dexter from Dexter's Laboratory. It has that intense tone at all times that I imagine for Sonechka, plus sounding nasally.
https://youtu.be/lknVbzyHL3E?t=9
Sonechka is from Russia, so a Russian accent would be big bonus points but is not required.
PRONUNCIATION
https://translate.google.com/?hl=ru&sl=en&tl=ru&text=sonechka&op=translate (Edited for the correct pronunciation, provided with the help of a Russian!
https://youtu.be/_VLGeKBTLkU