I completely agree with the need of having an story and quest linked to the custom character. Custom character need their own tag or tags that provide a personal story arc and quests.
And I like the idea that the personal story and quest are linked to the current origins so the "origin" characters become actual NPC's on the main custom character.
For example: If you create an origin story that is "tragic past" where your brother was killed by a vampire. And that vampire happens to be Cazador. As the story progress you might find out that Astarion did seduze your brother so Cazador could drink from him and that, in fact, your brother was turned into a vampire spawn just like Astarion. Then you might want to make a deat with Astarion to kill Cazador or might want to get revenge on both. Bonus points if you find that the best way to kill Cazador is using a Selune astifact that Shadowheart wants to destroy.
Another one: A soulgem was stolen. When the thief was caught in a ship, the sould gem was thrown into the sea and you just happen to find it. And in the process you absorved part of the memories of a netheresse wizard that might know how to solve Gale problem (or the opposite) and that many people are after. So if fact, you weren't randomly chosen to be a host, the Illithid were after those memories that lie dormant in you. You can have many people seeking those memories, from Zentarim, to harpers, to Cazador (if he is a wizard), to the order od schoolars in the underdark, etc.
You can be the son of someone who make a pact with the same cambion Wyll had but instead of promising their own soul, their promised "what they didn't know they have". Always though that it was quite cruel that kind of dealt in the Geralt world. They painted it as "not that big deal" and "the right thing" and the women who happen to be given in property as happy, but it could be interesting to see the other side. And play the person promised to a devil or even to a hero but not being that happy about being denied freedom...
You can be a Selune or Mystra choosen. Conflict with Shadowheart already provided. As a new Mystra chosen, Gale might be jealous and, maybe, allow for wizard characters some clever answers or at least say to Gale "Why are you telling me something that I already know?". Please, let the player be the clever once in a while. Specially if they have high intelligence.
There are plenty of opportunities for stories for custom characters and I hope they offer some. Otherwise, it would feel as those pen and paper game sesions where the master love so much the NPC's that the players are meant to be witness to their stories instead playing their own.
