WARNING: The following contains spoilers for Shadows House Episode 9, "A Birdcage and Flowers," now streaming on Funimation.
The stress associated with being a good servant and Face, combined with a non-reactive Master, has sent one of the girls of Shadows House on a downward spiral. She's amazed at how well the other children get along with their Masters (or that they interact at all) and knows very well that failing at the Debut will mean her end.
Since their very first appearance, Shadows House has been dropping heavy hints that Rum and her Shadow Master, Shirley, might not survive the initiation ceremony. Rum, Shirley's Face, is an almost pathologically shy girl who is also part of Emilico's cleaning crew. She has a good heart, but her interactions with Shirley are almost inexistent. Shirley doesn't speak, never addresses her and didn't even gave her a name. She's almost always eerily quiet, never expressing any needs or wants, and in Episode 9, Rum is convinced this is her fault.
Emilico tries to reassure Rum as best as she can, and succeeds. However, the audience, which can access other characters' points of view, cannot be put at ease. Ricky and Lou walk into Shirley -- who is immobile, with white threads sown through her dress -- and into a bush of poisonous flowers. Shirley doesn't ask for help like the other trapped children and doesn't even try to free herself, although it would have been relatively easy. Ricky and Lou find her incredibly creepy.
Outside the garden labyrinth, Edward, the master of ceremonies, has been going over the children's files... and finding Rum and Shirley very lacking. He's not bitter about the assessment, only objective as he points out that Shirley is extremely sedate has very low energy, barely eats, and worst of all, doesn't produce any soot -- the source of all the Nobles' powers. Edward doesn't think she will survive the Debut.
Shirley's lack of soot is interesting -- each of the Shadow children emits soot whenever they're feeling negative or intense emotions. As they grow, they become able to channel them into specific powers. For instance, Kate can use her soot to move objects, while Shaun makes it explode. Adults' powers range from controlling sound waves to crafting soot animals to brainwashing people.
While it could be argued that a lack of soot means Shirley is perfectly content and doesn't have any negative emotions, it might also mean that she doesn't have any spare soot to give up to channel any powers. It is very likely that the Noble Shadows are crafted from soot themselves, more sophisticated versions of the angry scorches and evil phantoms -- and these don't emit soot, rather, they just exist.
As every Face is supposed to save their own Shadow Master, which requires trust and collaboration, it is very likely that Rum will fail not through any fault of her own, but because her mistress won't react to her presence. And failing the Debut is a surefire way to get "repurposed" for a Face, which sounds incredibly ominous. Then again, Shadows House is technically a horror anime, and Season 1 has been slow-burning a sinister ending for eight episodes now. This usually means it's time to prepare for the sacrificial lamb.