Dokuhime

A manga by Mitsukazu Mihara, who also wrote Beautiful People and Doll, this is about a group of women raised from birth to be assassins and have had all their bodily fluids converted into lethal poisons.

Dokuhime starts with poisonous herbs under the cradle. Then under the sheets. And inside the clothes. Even mixed in the milk that they feed the newborn. This way the child gradually gets used to poisons and becomes the perfect assassination tool - the “Poison Princess”, whose every kiss, tear and even touch bring death. Her only chance of survival is to fulfill her duty as an assassin and find a way to live on in the enemy land to which she is sent… if her heart is strong enough.

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Tropes used in Dokuhime include:

• Acquired Poison Immunity: All of the Poison Princesses.
• Adult Fear:
• And Call Him George: The youngest-looking prince has a habit of accidentally killing things like pets, random animals, and his dad.
• Bad Boss: The Queen of Mitragnya.
• Can't Catch Up: This causes Lycoris and Hal to take a level in badass.
• Crapsack World: This is not a happy place.
• Fake King: Hal
• God Save Us From the Queen: The Queen isn't a very nice person.
• Half-Identical Twins - The triplets started out identical, but after the king's death they started changing (or not, in the youngest-looking one's case). The twins who hunt Lycoris are mirror-images due to one blinding herself to be her punished sister's other eye.
• Meaningful Name / Theme Naming: Most, if not all, of the princesses are named after flowers or plants, and usually toxic ones at that.
• Not So Different: Lycoris and Hal plus the two other brothers: one's a poison tester and the other keeps accidentally killing things
• Obfuscating Stupidity: Kait.
• Offing the Offspring: It is part of their mission to be through.
• Older Than They Look: Kait. He's 17, just like Hal and Mao, but he hasn't grown at all since he killed his father when he was 13.
• Poisonous Person: It's right there in the title.
• Royals Who Actually Do Something: What the Evil Queen is afraid of.
• Sadistic Choice: Most of the missions end up like this.
• Secret Test of Character: When the Poison Princess' queen first met Hal-as-king she set up a prank that involved poisoning people disguised as royals. He saw through it immediately and she's hated him ever since.
• Screw Destiny: Lycoris is going for this. So was the king, when he gave his two other sons the cursed mark and dressed, raised, and treated them alike; it didn't work out too well for him, though.
• The Evil Prince: It has been prophesied... maybe.
• There Are No Therapists: Justified in that it is the medieval period.
• Training from Hell: Childhood if you are a Poison Princess.
• Twincest: Zakuro; if nothing else, it is really heavily implied.
• Tyke Bomb: All of the Poison Princesses are these.
• You Can't Fight Fate: