You're literally hanging out with them constantly throughout the whole game.
There will also be companion quests I imagine.
Low key there kind of are. I mean like in the Blighted Village some of the goblins know Wyll and have a little chat which leads you to figuring out his past and motivations elsewhere. I assume the same thing exists for Shadowheart but I have yet to uncover the little Shar resort or the black riders camp which I assume will proc further insights into her character. I have heard a lot of people reference her amnesia but I haven't been able to shake that conversation loose yet. It all feels a little obtuse, I think it is amusing it is easier to get into her pants than her past, but I have to admit that is true of some people. Especially the more damaged ones, though somehow I doubt that was anyone's thought over at Larian.
