Angels Vermillion

The Angels Vermillion is a second founding chapter of the Blood Angels and one of the oldest chapters in the Imperium alongside it's brother chapters from the original legion.

Unlike its brother chapters who have maintained close ties with each other and their parent chapter, the Angel Vermillion are aloof snooty bastards who prefer to keep to themselves, whether it be from marines and non-marines. This is because every 50 years or so the chapter steals away mortals during the time called "The Sorrowing", where they render the kidnapped people unconscious, and place them in specially-prepared body bags in their Chapter monastery - "The Bloodspike". They would then exsanguinate the doomed mortals, draining them of blood completely and methodically, on specially prepared conveyor belts with special machines built to extract blood.

now for the longer version!

in the 'Eminence Sanguis' short story in the 'Dante' Special edition.

Basically Astorath, a captain, two of his guys, and the at the time high chaplain Hereon (it's set in the 400's of M41 and Astorath isn't the High chaplain yet) go to investigate the disappearance of civilian ships and refugees of a world liberated by the Angels Vermillion. They only very reluctantly only allow Hereon down to the world, and it was very tense. The chapter master of the AV says he'll send the ships back, but the people are (in fact everyone in the fortress monastery) are missing. Hereon basically demands to know why, and so he shows him. They have all of the civilians and chapter serfs hooked up to Blood letting machines in a ritual that happens once every fifty years called "the Sorrowing". Hereon freaks out, kills two of the Sanguinary Guard (who are painted red, not gold, and take on a more daemonic aspect) and then gets stopped. The chapter master says he doesn't want to do it but they found right after the Heresy that they had the thirst. They originally thought it was just them, and that's what started their seclusion (it was and is out of shame). But they fall to the thirst and rage less than most of the others.

Hereon criticizes him, and the chapter master basically says they are all doomed anyways, and that they save more than they kill, and that the Blood Tithe is a small price to pay for their greater service. He then explains how much they honor those that give their blood and they even kill a Sanguinary Priest to add the Blood of Sanguinius to the big pool of blood as a huge honor. Hereon once again freaks out and says he and Dante will expose them, and the CM basically says, "do that and I'll tell the inquisition all about our flaw, and they'll kill us (all the sons of Sanguinius)." He then lets him go and tells him to never return. He (the CM) continuously emphasizes that they ARE monsters, but that they aren't as bad, and they do it so that they can continue to save people and bring light to the shadow.

The Sorrowing is the chapter's solution for the Red Thirst, as they gather so much blood to drink that it lasts them until the next harvest. This is the reason for their secrecy. Only the Blood Angels know of the true modus operandi of Angels Vermillion.

So he just tells Dante.

TL;DR It's like the Blood Drinkers, except less severe and less frequent BUT sans the Daemonic influence and a hearty helping of needless shame.

Like most second founding chapters, they have had almost no fluff on them, until recently, with the release of the book "Dante" by Guy Haley.