it goes against the purpose of the party's goal
Wich is?
does not progress the plot in any meaningful way
And siding with Halsin progress the plot in what meaningful way?
there are no actual story related motives nor reasons whatsoever behind the decision to join her
Just bcs you dont have reason to do something, doesnt mean that there isnt one for anybody ...
But anyway as stated thousand times before:
- Astarion dont want to remove tadpole ... for him, cult is best bet ... your character can simply see it simmilar.
- If you play any Evil race, both Druids and Tieflings in the grove dont really treat you respectfully ... more like other way around, so simple revenge can be your reason.
- If you play Drow Male, and talk to dead True Souls Drow Males ... you will find out that in the cult of the Absolute Males are equal ... wich is something your character can greatly desire.
- Obviously any cult that have lots of followers have lots of potential power ... power your character can try to get for himself.
- Since nobody from the cult is turning, nor even know about tadpoles ... you can easily come to conclusion that they (read as their leaders) must know something about them ... therefore the best way to gain their secret, is to join them at least for a while.
And many more ... i shall wait if at least some of theese will get through.
Even if we count deep-undercover infiltration as a story reason, it is a terribly weak foundation for the premise since we are already able to fully infiltrate every single layer of the Absolute's army. Even Minthara and Nere end up being easily deceived as long as we pretend we are following the Absolute. So what is the purpose of joining her and acting like we're undercover when we already are doing that without an issue.
This is like saying you dont need (fake)ID to enter strip club ... bcs you allready managed to enter porn sides by simply clicking on "yes" when it asked if you are adult.
Why would Minthara or Nere question your affiliation?
Either you speak truth ... and you belong to them.
Or you lie ... but try hard to seem like belonging to them, therefore you are usefull and expendable tool.
Also both of them are quite certain of their own power, and their own forces that are in both cases all around greatly outnumber your silly party of 4 ...
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It's like the Gith Patrol.
You KNOW if you go there and let them know you have a tadpole in your head, they're going to crush your skull open and stomp on the tadpole. You don't KNOW for sure, but you KNOW in your gut it's true.
This is actualy good example.
Bcs as we know ... if you play your cards right, they dont just "not kill you" ... wich is also possible and not even that hard actualy, you simply cant go to them saying: "Hows hanging fellas, wanna hear something cool? I have your mortal enemy larva in my head!"
But if you play your cards REALLY right, they end up dead and you get all the benefits.
Thats why.
