Assassin's True Name is Charlotte Corday (シャルロット･コルデー, Sharurotto Korudē?). Charlotte Corday is the woman that assassinated the leader of the Jacobin faction in the French Revolution, Jean-Paul Marat.
The motive why she reached the conclusion of assassinating Jean-Paul Marat is quite complicated, but if it had to be said in few words, she'd say it was "to save thousands of people". Marat, who agitated the masses, and kept shedding blood for the revolution's sake, was seen as the ringleader of the chaotic France at the moment. Originally, it was a reckless plan that shouldn't succeed. But situations of fortuity/luck/contempt sided with her, and she eventually fulfilled the assassination.
It was later investigated whether there were collaborators in her assassination planning, but the, that it was concluded that there was almost no doubt that Charlotte Corday planned the assassination alone. She was executed with the guillotine, and the man in charge at the moment was Charles-Henri Sanson. In the way from the prison to the execution stage, Sanson traveled with her for about two hours, and admired her in his memoirs with "She kept a gentle and brave attitude to the end, and didn't expose fear or anger".
Due to her beautiful appearance, and her reputation for the skill to plan and execute an assassination on her own, she was praised as "The Angel of Assassination".
A cheerful, precocious, and active but humble girl. Her hobby is reading, and if nothing had happened she would have ended her life at a convent, and her name wouldn't have remained in history. However, due to the convent closing in the aftermath of the French Revolution, her fate changed.
Her weapon is a knife. The mysterious living being(?) that accompanies her is called an "angel" by Charlotte, but it can't be determined if it's an angel or not. Or rather, it can't even be determined if it's a living being or not.