Stormbringer

If a spell or ability instructs a particular object to deal damage, including the card the ability is on, then that object is dealing the damage, not the spell or ability. So Unyielding Spirit does stop damage from Void Seeker, Stormbringer, or Yasuo, Remorseless, but does not stop damage from Challenge, Last Breath, or Carnivorous Snapvine.

You'll start a noncombat showdown. (Hostile Takeover's reminder text is a little misleading in this regard-you have to have some kind of showdown before you can conquer.) This ruling applies any time you have a unit at a battlefield when your opponent still controls that battlefield, but doesn't have any units there. (Yes, that can happen. Hostile Takeover and Stormbringer are the easiest ways to do it.)