A friend and I were brainstorming about Sienna’s 4th career, and I came up with a potential career that is Warhammer lore-inspired and distinctly nuanced career: a Celestial Archmage.
In the Azyr section of the WH wiki, the Blue Wind of Magic is " a manifestation of the Aethyr’s reflection of inspiration and that which is out of reach." Sienna is constantly pushing her limits and testing her capabilities in-game, yet I believe what is ultimately out of reach for her is a sense of belonging and true purpose, as she (used to) roam the land offering her abilities for hire as a Battle Wizard as a means of income and merely to test herself. The page also mentions, “The magic of this Wind is based upon knowledge of the unknowable and the manipulation of the skies.” Though she has not consciously verbalized this, Sienna may ultimately desire near-omniscient knowledge which ultimately serves to further empower her magical abilities, not just in Aqshy’s realm of fire magic but in her entire existence, knowing what her limits are, fulfilling her potential of how powerful she can become on a tangible realm, or finally knowing what exactly has happened to her sister and others that she cared about prior to the End Times - something she has been unable to neither realize nor accept yet.
Reading a little more on Azyr and Blue Winds of Magic, the WH Wiki states that it is one of, if not the most difficult Wind of Magic to master, Sienna may potentially see this embodiment of magic as her true calling, given her proclivity towards power that she can wield and produce at will. Though fire magic in a destructive nature has been an addiction for Sienna, I believe the rush of power is what she truly love. Celestial wizards have incredible potential abilities, such as flight, control over storms, and other intangible powers - such as foresight and manipulating fate itself. Sienna might see this as the culmination to fulfill her true nature: embracing absolute power over mind, body, and the universe.
Basically, I believe Sienna’s 4th career should be a Celestial Archmage that wields lightning magic to her whim. Her first unique characteristic is that she hovers as a means of movement, rather than walks. The second could be changes in her appearance: red brands of Aqshy across her flesh is replaced with glowing runes of Azyr blue, and her eyes emit a vivid blue glow. Third, her robes are now elegantly flowing and a blue color scheme. She could also spout quips using her foresight about Bardin finding (or not) Karak Zorn, Saltzspyre’s now-questionable faith to Sigmar, Kerillians exigency, Kruber’s future in Brettonia, and finally her own potential future during the End Times.
As far as unique weapons at her disposal, the first one that I could imagine, appropriate to the career, would be a staff, held in her left hand, that enables Sienna to project chain-lightning from her right hand would be appropriate. This could have the unique capability to stun/shock enemies as
a form of crowd control, execute low health enemies, and when an enemy is executed below a certain health threshold, the lightning jumps to the next target and inflicts damage - which would either execute the target and jump again or simply fizzle out with that target (if this doesn’t include the “Unlimited Power!” Emperor Palpatine quote that only occurs uncommonly, there will be backlash.)
A potential passive ability that functions similarly to Bardin’s Ironbreaker “Gromril Armor” passive ability could be a lightning affect that stuns the attacker when struck, and other nearby targets depending on the amount of damage dealt by the attacker. If there are no nearby attackers, the enemy suffers damage as well as stunning them. Sienna would have to “recharge” this ability by using her lightning-staff up to a certain damage-well threshold, or by using her ultimate ability - of which I haven’t visualized yet.
I haven’t thought of a potential ultimate ability or any other passive abilities for her yet, these are merely the first that came to mind. If you have anything you feel is appropriate, feel free to add to the thread and see what we can come up with! Thanks for reading.