Possessed

The Exorcists of the Order of Saint Pencarrow couldn’t save you (or you didn’t want them to save you), so you made space for the devil within.

How did the demon come to possess you?

They were your imaginary friend. Take a fatigue to cast an illusory version of yourself somewhere within sight. You are at 0 Guard while doing this and you can speak and see through the double, but when touched, the illusion is broken.
You unwittingly cast it out of the Juniper Witch by following her steps. Take the unshapen lump (1 use) you stole from her hut as you escaped. Mold into shape and affix to permanently replace a missing body part. It has the tacky consistency of clay, even after attaching.
After you threw a party so legendary, hell heard about it. You can never get drunk. When affected by poisons or venoms, you can choose to take on a fatigue rather than suffer its effects. If you cannot take a fatigue, you suffer the poison’s effects.
Via a family heirloom, looted from a grave in desperation. Take a devils-ore helmet (1A) passed down by an ancestor who supposedly fought against the legions of the demon lord Zulon long ago and far away.
You were cursed by a school rival and failed all your classes. Take your school notebook, a debt, and a grudge.
You summoned it to help you cheat at school. Take a diploma (petty) and a diary thread (petty) which encodes a book’s worth of information at a time. The information can be retrieved by running it across a mirrored surface.

Blood. Whenever someone bleeds in front of you, you become deprived until you drink their blood. Attacks you make against bleeding creatures are enhanced.
Confusion. Take a sulfur stone. It stinks, but it makes the demon think it’s in control. Demons think you are one of them.
Prayers. Take warding circle (as spell (petty), in a Prayer Book (Grimoire, bulky)) which forbids demons from entering a circle you designate.
Bedtime stories. Take a shifting novel (3 charges), which can be used to create a small paper minion (4 GD, 4 STR, 12 DEX, 4 WIL). It can manipulate things, fold itself down, and follow simple commands. Using all the charges empties the book. Recharge: Wrap the empty cover around paper.
Coins. Any treasure you win, it wants half. You can sniff out the value of any item. Whenever you offer the exact value and allow the demon to take over (by taking a fatigue), the seller is compelled to sell you that item for the price.
Snacks. Take a package of gourmet desserts (10 uses). The demon has expensive tastes. You can eat any non-food object by taking a fatigue.

Go to Bonds to round out your character.