This is the story of a girl sworn to an eternal duty of ferrying wayward souls to the other side.

Long ago in ancient times, a town of death worshippers were brought to the brink of ruin by an accidental summoning of demonic spirits. Left with no other means to survive this calamity, the town offers up their youngest girl just barely twelve years to their patron god to save themselves. 

This saves the handful of them remaining but all that survive have been cursed by the spirits and will perish horribly in a mere few more months. Death agrees to leave the girl with them until their time has come but the girl's brother wouldn't have it. Diving further into the dark arts, the brother turns those willing into half living immortal beings.

Death angered by this travesty, commands the girl to slay the heathens and right their wrong but the brother overpowers her and they escape out into the world. Seeing her so helpless, Death grants the girl a portion of its powers but because she is still human the girl must put souls to rest to keep her existence sustained well enough to use them. If she were ever to use them beyond her limit, even Death would not be able to save her soul.

Her story takes stage across the world and over the millenia as the girl resolves unworldly matters for death while she hunts down her straying family. Every chance meeting they have shaves away a little more of their humanity away from them and they become more deathly beings. Tragedy had been the start of their respective journeys and only tragedy can bring them to their ends.

I call this one "Dead On The Run".

For the story rundown, it'd be mainly episodic with the girl persuading/forcing bound souls into giving up their regrets through a dream world where they can explore the past and contact the presently living. Naturally since these are troubled souls, each case is tough and they'll dig into old and fresh wounds and when the souls absolutely refused or fall in with the demons, she has destroy them and feed on them for power.

Sample content:
>A treasure hunter and a lost treasure that she has to track and destroy
>Royals that died trying to escape revolution that she has to guide to their rendezvous point
>A doctor who mercy kills his patients
>Another similar outbreak of demonic spirits in a mountain village that she saves but almost "dies" for
>A quarantine zone of people that think they're still alive
>An orphanage she visits every 5-10 years that ends with her staying for her friends' last days
>A future battlefield for soldiers bred into war
>Catching up with her clansmen and her brother continual escapes

Last two eps has her travelling with an AI machine probe in the distant future where humans on earth are dying out and her brother is making ghouls and demonifying souls to repopulate it. He's declared himself a lich king of a derelict supercity and has a very loose grasp of his own identity. 

Climax is from his POV as the reaper he's been running away from so long tears decimates his army with ease and he struggles in vain to remember why they're in tears when she finally has him dead to rights. Epilogue has her returning to the river their town used to be at to bury their mementos and her promising to return someday and join them.