Descendants and Weapon Proficiency can be leveled up to Lv. 40.
Upon reaching Lv. 40, a Descendant/weapon module socket type can be assigned, and assigning a module socket type resets the Descendant/weapon to Lv. 1.
You can assign module socket types at Inventory (I) > Descendant or Weapon Module Settings > Module Additional Settings,
and for more information, please check the Game Guide.
[Go to Game Guide]