A Superstar's overall strength is represented by their Power. Power is determined by several factors, including their Level, Gear Tier, Stats, and Ability Levels.
You can increase a Superstar's Power by:
Training them to raise their Level
Equipping Gear Pieces and increasing their Gear Tier
Upgrading their Abilities
Improving these areas increases your Superstar's core stats, including:
Attack
Health
Defense
Accuracy
Resistance
Critical Damage
Critical Chance
Speed
The stronger these stats become, the higher your Superstar's overall Power will be.