This information can be found in Geist: the Sin-Eaters
Quick info about applying the Geist Template, along with some commentary:

Notes on Vocabulary

Geist – synonymous with Sin-Eater. Geist (capitalized) is the combined and symbiotic entity, while a geist (lower-case) is the hitch-hiking entity which struck the Bargain with the Bound.
geist – the entity tagging along in the Sin-Eater's body. Not a ghost, not quite a spirit. Something different altogether.

Choose your Archetype

Choose your  Threshold

Choose two Keys

  • One must come from your Threshold
  • The other might be influenced by your geist

Choose your Manifestations

Record your Psyche

Re-allocate Merits, if desired and appropriate – remember to look at Ceremonies

Design your geist
Design your Keystone:

A Keystone is a gift from your character's geist. When you design your keystone, I need to know four things about it:
 1. What does the Keystone look like? How big is it? Size may affect pulling the keystone from Twilight, if your Geist is not always carrying it.
 2. Which Threshold is associated with it? You gain a mechanical benefit of three additional dice from participating in Ceremonies or Rituals if: a) your keystone is used as a ritual tool and b) some aspect of the ritual being performed shares an aspect with your keystone's Threshold. This does not have to be the same Threshold as your character, or as that character's geist.
Example: Justin Price, one of the Forgotten, uses Mortis Mask on a body to disguise the cause of death. The corpse before him is a victim of a very violent death. If his keystone has the Threshold of the Torn, he gains +3 dice on rolls made to perform this Ceremony so long as he uses his Keystone as a ritual tool. Alternatively, because Justin Price is attempting to disguise the death as a common heart attack, he could gain the +3 benefit if his keystone shared the Threshold of the Stricken.
 3. Which two Keys are associated with it? You gain a mechanical benefit of three additional dice from unlocking a Manifestation using a Key shared by the Keystone. The Keys chosen for your keystone do not have to match your character's Keys, but it will probably make your "life" easier.
 4. Which Skill is associated with it? You can spend plasm to boost any dice pools using that skill, gaining one die per point of plasm spent. You can't use this one weird trick to boost a skill over five, but you can do this even if your dots in a skill are zero, negating the unskilled penalty for any roll which takes advantage of this mechanic.

Storyteller's Notes about Keystones:

A keystone is an object that should be tied to the history of your geist. It is not something that should have belonged to your character, unless somehow your character and your geist have been in contact for the duration of your character's life.

Other possible changes:

You are welcome to use the event of your death as a reason to resolve any conditions or tilts you may be suffering.
Of course, it is also completely possible that dying has not made your character any more sane, stable, or likeable.


And Justice for All yskah