Emperor's Children

They worship Slaanesh, wear pink and black, and were part of the original first founding legions. They are the weird fat girl who has rape fantasies that no one will ever talk to because she's far too weird. There's always the temptation to be nice to that fat girl because you know she's desperate enough for attention to do some pretty freaky stuff if you asked that normal girls would dump you for.

NOT REALLY CHILDREN OF THE EMPEROR. They were unswervingly loyal way back when, which is how they got their name. Their Primarch, Fulgrim, was best buds with Horus, so when Horus did his heresy thing, Fulgrim went straight to Horus and said "Dude; what the fuck? For reals." Horus knew that Fulgrim was a perfectionist with mild OCD and, straight out of an 80's afterschool special, Horus convinced Fulgrim that he could get that perfection if he tried some of these diet pills... and meth... and speed... and crystal... and by the time Fulgrim was on cocaine he did a 180 turn and devoted himself and his legion to Slaanesh.

During the siege on Terra, the Emperor's Children got bored, broke off and went pillaging the civilians. Most of the innocents they found were ground up and distilled into drugs, anyone left over was raped to death. After the Siege, they dragged a shittonne of slaves with them back into the Eye of Terror. After snorting/smoking/raping/defenestrating/dogwielding them all up, they started stealing slaves from the other Legions, which started all the in-fighting. They did manage to steal Horus's corpse, and made at least one evil clone.

Marines of the Emperor's Children legions are always looking for the next high, and eschew tranqs and depressants (like booze) for hallucinogens and stimulants (like cocaine). It started out as a quest for perfection with performance-enhancing drugs, but now that they're full-blown corrupted by Slaanesh it's about peak experiences. Also have an obsession with noise, furry porn, tentacles and gettin' high.

The Pre-Heresy paint scheme for their minis are purple and gold, while the Post-Heresy paint scheme is pink and black. (Or pink and any clashing pastel colours.)