How to Be a Vampire

They were really good at killing though, each in their own way. It provided safety, and the girls knew. The Temple persisted on pushing them to be competitive of Father's affection instead of embracing their complimentary nature. Whatever familial affection they had was stomped out by constant trials. There was simply no room for them to be close no matter how hard they tried, AND TRY THEY DID, one was destined to prevail while the other had to perish.

Orin, before the BG3 events, had sort of accepted Bhaal's favouritism of his own flesh (Philomena, to note: her name wasn't that during her time at the Temple). Phil had exceeded all expectations, she was surprisingly both brutish in her work but also refined in her thinking. She was also the first to fully dismiss Orin in favour for her duties as a future Chosen. The only thing Orin could do was hope for a chance. Until then, she even worshiped Philomena, saw her as something Holy, second to Bhaal. I'm sure her countless Bhaal-imp killings were some sort of frustration let-out lol

When Gortash popped out of nowhere with conspiracies about taking over the world, it was the perfect chance. She noticed Philomena growing more and more paranoid from the moment he appeared. She started becoming existential, marking her Holy Flesh with inky markings and piercings... it was defilement. Phil's paranoia grew as the Temple started losing their respect, being also aware of their capacity for cruelty, perhaps even revenge. She also started fearing Orin, Sarevok, Bhaal. It drove her mad that, at such a pivotal time of her career, a plan to take over the entire world, she would start breaking apart. She wasn't ready for it, and everyone knew.

It didn't take long for Gortash to gift her an ornamental, pristine set of armour, everything that Philomena isn't. She never took it off, and the Temple was now furious. Orin even more so. How dare she hide HIS CREATION from his worshipers? Philomena's divine flesh is not her own, after all!