Metaphor: ReFantazio

At the core of Metaphor: ReFantazio’s combat are Archetypes. Archetypes are effectively Metaphor’s class system, acting kind of similar to Personas in the Persona franchise.

To get this achievement, you simply have to reach rank 20 in one Archetype, which you'll absolutely do at least once, especially if you want access to the more powerful Archetypes. 

Once you've mastered one, the ‘Archetype Adept’ achievement will unlock.