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jeanne trevelyan buys into being andraste's herald full-force. she was the youngest of 13 (twins with her brother, mace; several of her siblings are half-siblings from her father's first marriage), and her maternal grandmother is a fierce player of orlais' grand game. she meticulously married off her non-inheriting children to try to cultivate influence in all corners of thedas, with jeanne's mother being married to the widower trevelyan due to the comparative size of the trevelyan clan.
jeanne herself had three potential paths in life, according to her grandmother: marry an influential man, join the clergy, or become a templar, with grand-mama much preferring that she join the clergy. because, you see, grand-mama had always hoped one of her grand-daughters would one day become divine, and with jeanne's age and the divine's age, she hoped jeanne would be that grand-daughter.
in fact, mother giselle and jeanne are already in contact long before the events of the game, as jeanne's grandmother had introduced them in the hopes that mother giselle would become something of a mentor to jeanne.
all of which is just to say: in all the ways that dhavi is exactly what the chantry doesn't want their inquisitor to be, jeanne is exactly what they do want her to be. or so they think.
because even when the spirit of the divine tells her that it wasn't andraste who led her out of the fade, jeanne decides andraste was merely acting through the divine, that she's still chosen—she continues the facade of being andraste's herald even after being told otherwise. and instead of letting cassandra, leliana, or vivienne become divine, she ascends the sunburst throne herself.
the worst part, however, is that she begins donning masks as divine, participating in orlais' grand game even though by all rights the chantry is meant to be above mortal politicking. she aligns the chantry even further with orlais. she is just... the utter opposite of dhavi in all meaningful ways.
in her playthrough she romanced cullen and ignored his arguments when she decided to go down the templar specialization even after she knew about his addiction. she doesn't encourage him to continue taking lyrium, but she doesn't shy away from taking it herself.
which might have something to do with the masks.
all of this is just to say: toxic divine!jeanne/right-hand-of-the-divine!cassandra. jeanne brings out the worst in cassandra and regresses her throughout the events of inquisition. i'm so sorry cass.