Murasakiiro no Qualia (Qualia the Purple)
Qualia the Purple is a SF light novel divided into two parts.
In the first part, we're introduced to Hatou Manabu, the main character, and Marie, her friend. Marie claims that she sees all living things - humans included - as robots. We watch as Gaku (Hatou Manabu's nickname) learns and explores the extent of Marie's "eccentricities" as they become involved in a serial murder case.
In the second part, we see Hatou Manabu slowly and spectacularly breaking down as she seeks, in order, truth of Marie's death, vengeance, and finally a way to defy Marie's fate. The extent she's willing to go to achieve this will put Okabe Rintarou and Madoka to shame.
One of my favorite quotes from part 2:
"That's why, I will forgive you in this world, love you in another, and hate you in yet another.
I will help you, reject you, support you, break you, betray you, and use you to my end."
This LN has been adapted into a 3-volume manga series, as well.