Evolve into a stronger form
Evolution spends gems and materials to turn a unit into a stronger form with higher stats. The efficiency comes from carrying harder waves and farming faster at endgame.
A dated EN beginners guide (2026-08-15) confirms the core: evolve your units to unlock stronger forms and progress faster. Evolution is the step after starring — where a unit that has hit its current form's ceiling takes a step up into a form that can clear what the old one couldn't.