Hey guys this is the fluff for my nurgle marine army the plague lords. I dont know a great deal about marines fluffwise but here goes.
The plague lords orignally did not start as one legion but was orignally 5 seperate chapters, these chapters are the emperors crows the emperors wasps the aqua hawks the shadow ravens and the storm knights. These 5 chapters captains chapter masters librarians and chaplins was proud and very strong willed. As a result of their proudness they would fight one on one against the enemy leader if it meant certain death.
The first chapter to become part of the plague lords was the emperors crows. For a long time they had wished to find a way to become immune to pain and disease, as they had seen many other chapters warriors succumb to plagues. However this was to eventually lead them to a mysterious inquisitor who said he would give their head librarian a book which contained the secret to what they desired. To them this was worth a try as everything else they had tried had failed. As they returned to the fortress monestrary the head librarian read one of the pages of the book out loud. Without realising it at first he had just started a warp storm which would spread to their home system.
As he left his quarters he realised what he had done, he had put his entire chapter in danger.As he went to spread a warning plagues began to creep inside their ships and he quickly realised it was too late. He realised they had 2 choices either they swore themselves to nurgle and he completed the spell or they all died. Seeing the head librarian just standing there the chapter master engrim diehard commanded him to complete the ritual as he would rather sell him and his chapter and all 4 of the other chapters that had joined them die. As the head sorceror completed the ritual the commanders of the other 4 chapters mysteriously died. After the ritual was completed all of the marines was wearing the same bright sickly coloured armour with dark tints, their back packs had turned blue via the viruses and as the ship landed nurgle had guided them to the daemon world of nurglicous. As the marines got off their ships Engrim declared all the marines to be under his conmand and changed his name to kugath the prince of plagues and changed his chapter now legions name to the plague lords