Ah, I see, then maybe instead of the whole lost primearch thing they are instead a chapter with a history that no one knows except for them and they disappeared during the Heresy and suddenly emerged during the 40th millennium. They have a deep hate for Fulgrim and Slannesh because they were almost completely destroyed by the Emperor's Children during the Heresy. They only recruit from rich planets, mainly from Cupidius (my made up planet) because of their hate for the poor. No one knows why they hate the poor so much but it may link back to their homeworld. They are also very curious people and secretly make deals with Xenos and Chaotic forces and have a big collection of forbidden Artifacts in their secret museum. Their current Chapter Master is Percival Ravenaught, a very silent man with a surprising sense of humor because he make the dumbest jokes when you least expect it. They also have a weird way of thinking and absorb information at an inhuman rate, this is mainly why their thirst for knowledge is so strong. They are also nocturnal and preform exceptionally better during the day. Their tactics are aggressive and fast and love to use loud noises to alarm their enemies and cause massive damage then run away, leaving their opponents in a crippled and confused state. Their colors are mainly Gold, Brown, and White and their weapons are painted a bright gold. The gold also helps them since it blind their opponents during their hit and runs giving them more advantages over their enemies. Their logo is a wing of an owl with a gold eye in the middle. What I am going with when it comes to this chapter is a group that are rich douchebags that are morbidly curious and open to allying with Xenos and they hate Slannesh. Their battle cry is "Our toe is worth more than your pathetic lives!"