I only knew Us for a tutorial I kept reloading until I was sure what was up with the brain, but if anything ever happened to him (I'm guessing he's a he?) I would kill everyone in the Forgotten Realms, and then myself.
@canthidium@Herowyn in the room before you go outside and meet Lae'zel on the Nautiloid there is a platform with an interactible "button" that takes you up.
There is a person with an exposed brain in an operating chair there. If you pass the skill checks, you get "Us" as a temporary companion to support you in the upcoming battles (until the Nautiloid crashes).