Ok guys, I locked a concept:
Mechanically she's a human Dark Presence Eliciter, specialized in buffing allies, debuffing enemies, and healing. Her strength lies in the fact that she has exceptionally good action economy, so there's never going to be a turn in which she's not contributing something. Her bread and butter is to completely lock down enemies by using mind-affecting effects, but she also has multiple ways of making her companions stronger, so even against mind-immune enemies she's going to have something to fall back on. Below the build I have in mind so far:
[ +- ] Build
Stats
Str 12 - Dex 16 (base 15+1 lv 4 ASI) - Con 14 - Int 8 - Wis 10 - Cha 20 (base 17+2 race+1 lv 8 ASI)
Talents
Lv 1 - Personal Conflict (drawback, taken twice)
Lv 1 - Totemic Aura
Lv 1 - Call to Arms
Lv 1 - Mental Assault
Lv 1 - Totem of Doom
Lv 2 - Looming Darkness
Lv 3 - Life Sphere
Lv 4 - Greater Invigorate
Lv 6 - Deeper Healing
Lv 7 - Restorative Cure
Lv 8 - Finish (Rally)
Lv 10 - Replenish (Rally)
Emotions:
Lv 2 - Touch of Apathy
Lv 5 - Lethargic
Lv 8 - Stupor
Feats
Lv 1 - Extra Magical Talent: Dark sphere
Lv 1 - Black Totem
Lv 3 - Impassion
Lv 3 - Soul-Piercing Gaze
Lv 5 - Extra Emotion: Touch of Joy
Lv 7 - Extra Emotion: Lingering Joy
Lv 9 - Extra Emotion: Touch of Rage
Martial Tradition: Staff Master
In terms of fluff, I was thinking the idea could be this: you guys are long-time friends, adventurers who've worked together for a LONG time. One day you find this lost, wounded, amnesiac little girl, and decide to take her to your HQ in order to help her: it soon becomes apparent that a) she's shockingly well-trained for combat, considering her very young age and b) she has serious troubles processing emotions... And when her emotions go haywire some ridiculous power is unleashed. So you decide to keep her around because, well, the alternative is letting such an unstable girl wander around alone, and so the campaign begins: the modules we'll play could be various missions you'll take on as part of your job (with the girl tagging along), but there could also be an overreaching plot of "investigating the truth about the girl". I myself don't know what this truth would actually be, I'm gladly leaving this to the DM in order to be genuinely surprised: ideally, this truth should tie into whatever major villain whose plans we end up thwarting. In many ways such a narrative structure would be similar to how Fairy Tail works, dunno if you're familiar with that manga.
Anyway, how do you guys (both players and DM) feel about doing something like this? For me this would be the biggest challenge in my career as roleplayer: playing an emotionally insecure child with an
ambiguous disorder (played seriously). I was actually thinking her alignment could start out as True Neutral, and then evolve over time as she spends time with the party and her personality is influenced by them.