Theme Skills are a new feature introduced in December 2020. These skills act similar to Type Skills in that when you have two or more Sync Pairs together in a team, the effect will activate and you'll have the boost
Unlike Type Skills, however, these skills are determined based on the character including things like if they're a Gym Leader, from a specific region and so forth.
Like Type Skills, Theme Skills can be powered up using Skill Spheres
|Battle Facility Foe