This trophy will unlock upon completing the following side missions, which can be found in Flood Town and Gas Works:
The Big Chill
You'll pair up with an Ice Conduit, who compared to his comrades does not agree with their methods and hopes to redeem himself by helping you out clean up the Ice Army. These side missions serve as a mini sidequest and are linked together so you'll know it when you activate these missions.
Note that these four side missions are labeled as Good Karma opportunities , so unless your karmic rank is maxed out as Infamous on your Bad Karma playthrough (karma won't change if its maxed out), consider doing these on your Good Karma playthrough instead.