Infamous serial killer Dr. Quill has murdered dozens of fillies and mares, as well as some females of other species. He'll target anything with female parts, paralyzing them with poison and using their bodies like love dolls as they slowly die of thirst. He then throws them out and finds another toy to sate his wicked desires.

He avoided capture for a long time by moving from city to city and choosing unimportant targets that few would miss. But then he made the mistake of moving to Canterlot. Then he made the mistake of targeting Celestia's newest filly protege, Nightfall Gleam. He always expected to be caught eventually, and fully intended to laugh off his own execution, but will forever be sorry once Celestia's revenge is complete.

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Contains: foalcon rape and snuff, karma, necrophilia, castration, gratuitous OC
Details
Chapter 1: Potential Lost: alchemy, fear, imminent rape, imminent snuff, mind destruction, talking to strangers, unsupervised child
Chapter 2: Innocence Destroyed: bondage, choking on dick, cervix breaking, cunnilingus, filly sex toy, foalcon, it's best when you hear the pelvis crack, irrational belief that you will not regret this, mind destruction, oral, proper care and cleaning of fuck toys, rape, sadism, straight, vaginal
Chapter 3: Life Ended: bath toys, blood, breaking a toy, corpse toilet, cum guzzling, dehydration, foalcon, mind destroyed, necrophilia, rape, snuff, still not regretting it, straight, taking out the trash, tape gag, waterlogged corpse, vaginal, watersports
Chapter 4: Rage Ignited: anger issues, earning promotion, freshly used corpse, freshly used almost-corpse, implied rape, ironic disappointment at a lack of murder-rapists, gotcha, momentary Daybreaker, shape shifting
Chapter 5: Judgement Passed: cheap sex toys, following orders to the letter, fuck the law I'm Princess, hot nurse, imminent castration, implied sex changes, lying to the public, masturbation, non-spectacles, plans backfiring, promotions, tools of the trade, who needs pain-killers?
Chapter 6: Justice Served: annoying child, blinding, castration, cum eating, gore, justice, literal (for once) fleshlight, more gratuitous oc, painful erection, shaving, state-sanctioned torture, surgery without painkiller, unethical use of prescription medication