I think it is possible to come up with a rationale for a Ghost PC. Magic is very unpredictable and can cause all kinds of craziness. For example:
My character was a young troublemaker who inadvertently released a Dennarion when he broke into his Warden father's vault to show off for his girlfriend. She was possessed by a Denarrion when she picked up a coin and proceeded to start a ritual using my character and his sister as sacrifices. Luckily his father had been alerted by a tripped ward and with the help of my PC drove her off. Unfortunately, the father's spirit was stripped from his body (which lies in coma) and somehow bound into his Warden's sword. He haunts his repentant son who wields the Warden Sword and is doing his best to make up for his checkered past.
Here is the write up my GM gave him:
JOHN FRANCIS YOUNGBLOOD JR.
TEMPLATE: SPECIAL
HIGH CONCEPT: MOSTLY DEAD WARDEN HERO
TROUBLE: MY SPIRIT IS TRAPPED IN MY SWORD, MY BODY IN THE HOSPITAL
ASPECT: I MAY NOT BE A GREAT DAD, BUT I LOVE MY KIDS
ASPECT: DID I FORGET TO TELL YOU…
ASPECT: LOOK AT THE LEGS ON THAT ONE
SKILLS (+39)
SUPERB +5: Presence, Contacts
GREAT +4: Discipline, Lore
GOOD +3: Conviction, Rapport, Weapons
FAIR +2: Athletics, Burglary, Stealth, Scholarship
AVERAGE +1: Deceit, Investigation, intimidate, Alertness
POWERS (-11)
SPIRIT FORM [-3]
THAUMATURGY [–3] (page 275)
SPECIALIZATION.
Anti-security magic Complexity Bonus +1.
Physical Immunity [–8]
The Catch 3]
Spirit magic and exorcism- Magic [1], everyone knows to use just about anything non-physical.
TOTAL REFRESH COST: 11
CURRENT REFRESH: 11