Book II introduces the Nifl and Muspell kingdoms, focusing on the conflict between Fjorm and Surtr. Enemies in Book II are generally stronger and have more complex skill sets. You'll need to start thinking about team synergy and specific counters. Consider investing in your favorite heroes by leveling them up, teaching them skills, and merging them if you have duplicates. The 'Sacred Seals' feature becomes increasingly important here for customizing your units.
