Meet Lancrelus, from Last Hope
Lancrelus was a Raven Guard, specializing in infiltration. He was a First Born, and when the opportunity arose to become a Primaris, he decided to cross the Rubicon alongside his squad brothers.
Unfortunately, the genetic defect of his lineage was activated, and a terrible hemophilia nearly ended his life. His brothers did not survive the process.
Since then, he has lived with the sword of Damocles hanging over his head. He knows he suffers from a disease incompatible with battle, but the genetic drugs that Alessio is creating for him help him survive battle wounds.
Luckily, his brother Ramu has taught him well how to be much more efficient, agile, and skillful, to avoid being wounded in combat.
He fears death, which is a cardinal sin for an Astartes. Although his best friend, Calanos, doesn't seem to condemn him for it.
He joined of his own free will, later discovering that his name was inscribed in the Book of Destiny.
He believes in justice and second chances for those who have lost their way…
One curious thing about him is that he's always eating. He has a sweet tooth, although he says he eats so much to compensate for his hemophilia and blood loss… which doesn't change the fact that he's a glutton and could buy his knowledge with sweets.
He's a gossip, and he knows everything of what happen in Solar Pilgrim, the chapter ship of Last Hope. Especially since he's extremely quiet; few notice him when he's around, and he usually hangs around the latticework of the ship's galleries, where he observes without being seen.