The Familiar System is a feature that allows you to obtain special cards from monsters, make them stronger, and gain special bonuses while summoning them. Roro the Familiar Manager, a sentient handheld device, is given to every character by a Mysterious Man and his aide, to research and track all of the cards you collect. Many of the monsters you hunt will have a chance of dropping a Familiar Card (also known as "familiars") when defeated, and consuming these cards will allow you to summon that monster to assist you in battle, while also providing 2 random potential bonuses. At first, you will only be able to summon one familiar at a time, but you will be able to unlock two additional summoning slots as you progress.
As you collect more and more familiars, you will start to fill up Familiar Badges, which work as special sets dedicated to each area. Each set can give special bonus stats that will apply to your character (up to a certain amount at a time). Completing 1 Familiar Badge will unlock the 2nd Familiar Slot, and completing 10 will unlock the 3rd Familiar Slot.
The sets listed in red cannot be completed without a Familiar Booster Pack.