Reese Adams. BG3.

While she is generally 'good' aligned, she's also very malleable and influenced by the people around her. Between her late adolescent years and the events of the game, she was pretty closely structured, probably paired off with someone that was her guardian (possibly lover / life partner) kind've like the Warder's in WoT with their magic users, to keep her from straying too far from the light side of her abilities, to make sure she didn't come under undue influence or get snatched up by a cult that wanted to make use of her abilities. I'm running with the general idea that whomever that was died (or she presumes died) in the Illithid crash. In verses where she's the Tav, story plot progresses as canon. In verses where she's a supporting cast member or that we go with an entirely different course of events for plot purposes than what we see 'on screen' in the game, she will have wandered away from the crash (maybe even was flung somewhere else entirely not even in the primary starting location) and ended up wandering around for a while on her own until she runs into your Tav or (in the game npc) or OC or whatever and then the story can progress from there for whatever aspects of the plot we would like to explore.

I am absolutely fine with darker themes of corruption & toxic relationships if that's a plot line you're interested in - there's a few things I won't write but are part of her history (csa & n*nc*n are things that occurred at one point or another in her past, but will not be seen on screen other than mentions of plot points if the relationship with Reese & your character reach that point, or it's seen in a mental connection etc.).

At the base of all her decisions, when she's making them on her own is the thought of: I don't want to be the villain in anyone else's story. This, of course, means that there are times when she is going to have to do violence and hurt people to stop them from hurting other people / people that can't protect themselves / people that she cares about, and she's (generally) okay with that. It might haunt her sometimes, but she is used to living with regret and ghosts so what's a few more?

That is Reese as the Tav, as the lead. HOWEVER. It is important to note that Reese is incredibly love starved, affection starved, touch starved (outside of sex, which she pretty much never passes up because it's a pretense of affection) and as a COMPANION she is very malleable. She latches on quickly, becomes smitten and pines from a distance with gusto and she will very quickly come to crave the approval and affection and love (toxic or not) that she sees as a potential reward for her loyalty and her helping the MC obtain whatever goal they have.

She does drift, fairly easily even, to lighter or darker sides of the moral scale without much effort. Even the smallest signs of approval and affection for making a choice that makes the MC happy and she's floating for days (or until the first perceived sign of disappointment). She may try to tilt someone who's bent on mass destruction or world domination into a less toxic and dangerous path at first, because that just doesn't seem all that !neat! to her, but it does not take long for those protests to diminish if someone is taking the darker road. On the opposite side of that, if she's in a companion role and the MC is set on saving the world at all costs, Reese is going to be the first one to step up and say it's okay, I will be the one to set off the bomb in my chest or whatever other device of mass destruction that will end her but end the Bad Guy / Threat because she would see that as the most noble sacrifice she could make for her MC and the world, and the world clearly needs pure hearts like the MC than they need a broken, damaged thing like her.

The headcanon here relates to some higher power / entity (typically one with dark purpose) latched onto her and infused her with a seed of its own power, leaving it there to fester and grow until such future time as they could manipulate her to their own ends by influencing their opinions, thoughts, desires, visions etc. until such time as they can use her to their best advantage. In her original “canon” it was Darkseid but any deity or entity works just fine in this verse. (If you play one of the trio with the crown, for example, this could be your character’s deity, for example, and can use that connection to exert influence over her through the power that has grown in her over the decades.). It could also be a deity like Shar or whomever she starts out as an agent / priestess of or it could be an entirely heretofore unknown entity. I’m literally up for whatever plots with this.

                                         I will not  b r e a k. 

                 Treat me as your canvas, leave your                 mark… your painter’s signature across                                          my skin.