Every player is assigned a family before the tutorial in Roblox Demonfall. This occurs during character customization and each player receives three chances to roll a new family. It's important to understand the family you are assigned because it affects the type of build you should create further in-game.
Each family receives their own passive abilities and buffs, which greatly affects the strength of the Demon Slayer or Demon you will become as you progress. Once established after character customization, you cannot change your family in Demonfall without wiping your character and all the progress you've made thus far. This is why it's important to understand each family's buffs / passives / abilities prior to starting your journey.
