Hmmm... lots of choices.
I've not seen the series with Shion Sonozaki, so don't know how she compares.
Here are some of my nominations.
- Lucy from Elfen Lied
- Sakura from Fate/stay night
- Himemiya Chikane from Kannazuki no Miko
- Yuna Miyama from Maburaho (as she seemed in the end)
- Akane Tendo from Ranma (sweet girl, but a violent maniac, per Kasumi)
- Kaede Fuyou from Shuffle (during her breakdown)