Besides the companions, which npc in bg3 do you think has the most tragic story?
Interesting question! A lot of NPCs have some pretty tragic backstories and outcomes, but assuming you play a morally good character and help everyone you can, I'd say probably Art Cullagh.
Poor man was just an honourable Flaming Fist who enjoyed playing the lute in his spare time. He went to the Shadowlands to investigate a Sharran cult and ended up stuck in a 100 year long nightmare with only a spirit for company. Then, when he woke, he learned that everyone he ever loved was probably gone, the Flaming Fist fell off, and Thaniel (his only friend) might be dying. He lived long enough to see the shadow curse lifted and Thaniel set free, but he never recovered. Instead, he slowly withered away, succumbing to the toll the century-long curse took on his body, until he was so weak he couldn't even eat or hold quill. ☹
Flaming Fist Outpost 3. Ubtao Shrine
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The Flaming Fist have discovered a shrine with a statue of Ubtao upon it. The leader of this militia has decided to steal the statue to impress the higher ranks of the faction. Nearby Tribal Warriors consider the shrine sacred and protect it at all costs. Will the players aid the Flaming Fist to improve their renoun with the faction or aid the tribal warriors and be bestowed a temporary blessing? Desecrating the statue may bestow a curse, while aiding the tribal warriors may make an enemy of the Flaming Fists. The choice is yours!