Azumi was working covertly to undermine the Sha from her base of operations after being hurt by them. The Sha discovered the plot, assumed Guy was in on it, and attempted to kill them both. After discovering Guy was NOT part of it, they still killed Azumi for her treachery and stole the baby to bribe Guy. Guy instead slaughtered the assassins and fled and could not be contacted.
A Sha assassin, one of Guy's friends, hunt him down, find him and proposes a deal: Kill the Guildmaster and allow the Sha to rule the North, or refuse and lose his daughter. Guy contemplates the idea, and the assassins tells him about Azumi and Guy finally realizes the point of her death.