Quote Originally Posted by Errorname View Post
Spoiler: Bhaalspawn
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Considering that you can play as one and that Orin can potentially be the main character's sister, no they are not pretty much irrelevant to the game's plot. They can be depending on how you play through a Tav run, but they're an integral part of the Dark Urge plot.
Spoiler: Bhaalspawn
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That is an optional sub-plot that only happens for one particular version of the main character. That is not the main plot at all. The main plot doesn't care about Bhaalspawn in any way, and would happen without them basically the same as it does with them.