31 Days of Halloween: C.C. (Code Geass)

C.C. aka The Gray Witch is apparently immortal, healing from any wound (implied to include beheading) with enough time. She also doesn't age. Apart from her immortality, C.C. has the ability to bestow people with the power of Geass, which manifests differently in each person but generally carries the ability to affect the minds of those it is used on in some way. The Geass sigil glows on her forehead whenever she manifests this power, and she has a similar scar on her left breast. It is hinted that many more like her exist, as shown in her memories of many children with similar sigils, and she suggests that the power has precipitated bloody conflicts in the past. Her powers caught the interest of Britannia, who imprisoned her for experimentation purposes.