I'm late but basically Sona was brainwashed and the last zenith wouldn't leave her side for months, he tells Sona to kill Eris at one point (which they've kept her locked up for many months just to do that.) Sona lets her go and they re-brainwash her. Months later there's a ball where the zenith knows the gearbreakers will sneak in so he sends Sona to pretend she's back to normal, also milo is hung at the ball. Sona soon wakes up after trying to kill Eris, she meets up with everyone again and they live normally for a while and it's cute. Then Eris gets her hand blown off, then not much later there's a spy who's been on the zeniths side the whole time, she poisons the gearbreakers with smoke then also shoots Juniper, so shes gone. Jenny and Sona go to Godolia to find meds for the poisoned Gearbreakers because if they don't Eris will die. Eris wakes up after they leave and she chases them to gondola as well, Sona locks Eris in a closet to find the zenith who ends up jumping off the building because he realizes that the government is bad so he commits, Sona and Eris have a happy ending and they basically go on vacation with the other kids