A core component of Fire Emblem Engage's gameplay revolves around the progression of individual units, which players can customize further by unlocking new weapon proficiencies that work around restrictions to weapon types based on classes. By adding variety to the number of weapons units can wield, players have far greater depth to their roster of characters for battles ahead without even factoring in the unique advanced classes gained later. Although certain proficiencies demand specific Bonds to be obtained, players that explore this option can have a broad collection of far better-equipped units than their base affinities would allow.

https://screenrant.com/how-to-unlock-weapon-proficiencies-fire-emblem-engage/