She’s a tribe of one villichi (multiple personalities), the result of an infant mind shattered by abuse. Being brought to a convent, an environment free of abuse, where she was cared for and made friends, even sisters, saved her sanity.
Tribes of one are a rarity in the best of cases, but her specialness came to her at puberty–the power to imprint those personalities unto the minds of others. The power reared its head in moments of panic, pain, or anger, resulting in multiple cases of temporary madness and perhaps a death.
The girl could have eventually gained control over the power had she been taught mental discipline and emotional control, but in anger her high mistress instead exiled her, wiping her memory of the convent and its location. She did this at a time the girl was especially vulnerable, confused and plagued by guilt for the things she had done, even if involuntarily.
Instead of receiving the support and love she crucially needed she was cast out and the only good memories of her young life erased. She has gone through denial, sadness, and finally rage.
The passing Dragon sensed her psionic rage and pilfered her life story from her mind. Seeing great opportunity there it proposed to grant her power to exact revenge in exchange for rooting out the convents, for the Dragon saw the secret power that are the villichi as an unknown it needed to get rid of. Without the convents, future villichi would be unorganized and powerless to oppose its plans.
She was given power and the means to call upon the Dragon when locating a convent so it can come and destroy it.
So I seek help about the story itself and the power she was granted. I’m stuck in a circle of ideas.
Maybe she’s just a normal villichi with the otherwise rare condition of ToO. Maybe she does something horrific, like kill one of the sisterhood in a moment of rage, then has her memories wiped and gets exiled. She seeks revenge from her exile, but doesn’t know where the convent is anymore. Something or someone finds her and does something to her that causes her personalities to jump out of her mind into the bodies of people, allowing her to create an army. Does it only work on humanoids? Women? Humans? Does it first drives them mad, then kills them? Does it aninate their bodies? Is this undeath? Is she undead?
A few plot holes. With ToO, both the Mistress of the Convent and the Dragon would need to scan for, isolate and manipulate each personality. It is extremely likely that one or more of her personalities retain her memories. A Villichi would never work with the Dragon as they are dedicated to the path of the preserver and the way of the druid, so even being manipulated by the Dragon there is still a good chance she’d switch teams. At least one (if not all) of her personalities would be fighting against the Dragon’s will.
As for abilities, I would suggest the schism psionic ability to represent the capacity for her personalities to act independently with spells or psionic powers while another personality controls her body. The fission psionic ability would be a fun way to let her personalities manifest in their own physical bodies. I guess another way this could be done is with Astral Constructs, but they’d be weak by comparison.
A rogue villichi actively seeking to destroy convents in the Ringing Mountains would be a dire threat. Convents would reach out to allies like druids and the Veiled Alliance to launch a kill team to eliminate her with extreme prejudice.