Companions are characters that adventure alongside your character. They could be a mentor, a sibling, an animal friend, or really anyone or anything with whom you've formed a lasting bond. There are two types of Companions, Helpers and Allies, and your character can have any number of each!
Helper companions just have a background that describes them, which can be used like any other background on your character sheet to assist you in tests. Because helpers are just a background, they generally don't have to contend with risks from tests and are often small or can hide away somehow.
Allies are a bit more complicated. Allies have their own pool of damage, attributes, passive attributes, items, and their own background. However, allies only progress when you do and cannot have their own potential. Because allies have their own health, attributes, and items, they're almost another character! Expect them to get into scrapes and have to contend with risks.
There are also a few rules to remember when playing with allies:
Allies share injuries! While they may have their own pool of health, you share injury boxes and their associated injuries. Maybe you magically all get hurt in the same way when something goes wrong, or maybe each ally has their own specific injury. At the end of the day, you get to decide why this makes sense.
Allies are defeated together! If one of you goes down, you're all out. Maybe the allies beat a hasty retreat when things start looking bad, or maybe the final blow that hits one character comes mere seconds before the danger that befalls the rest. When the defeat happens, go with whatever makes sense.
Allies share backgrounds! Allies can only ever have one background of their own, and they can use any background on your character sheet that references them.
Allies get healthier when you do! Whenever you spend potential to increase your health by 1, you increase their health by 1 as well.
Allies share special abilities! As long as it makes sense to do so, allies can use any of your special abilities from your character sheet. You can even make teamwork-based special abilities that rely on their presence!
To make an ally, answer the creating a character questions, but skip What Makes you Unique?, since allies share your ability points and other unique stuff. When you get to What is your story?, think of a phrase that sums up this ally. Then, instead of taking the pool of potential, write that down as the Allies' starting background. They can never have more than this one, but you can feel free to change it any time it makes sense to.