Long ago, an ancient and powerful lich created a new spell that bounded his spirits to the blood of his kin. So long as any one of his kin remain, his spirit will still persist in the world even long after the death of body. Centuries have passed and the lands he conquered and the empire he built have fallen into the hands of others but in their place, a new religion serves his immortality as he serves as its god. Having accumulated arcane knowledge over the lifetimes he's lived, his followers and his kin are able to summon forth his spirit and borrow his power to solve their problems. Not everyone can just do so though as it takes learned spellcasters to call him forth and a sufficiently powerful vessel that inherited his blood to contain his essence for the appropriate amount of time. It is those two conditions that this story revolves upon.
A young man who's been trained up in the religion's temples finds himself in a peculiar bind. He has served as a traveling apprentice cleric alongside his troupe and it is clear that the lich's blood expresses itself strongly in his features but one night an emergency required a vessel to summon their god and they chose him to fill the role but no matter however they tried, his fellow cleric just could not summon the lich through him. Even though he has successfully summoned the lich many times before, he himself appears to be an especially unsuitable vessel for the being. This contradiction in his being results in the loss of their comrades as only he and the attempted summoner lived through the crisis.
The summoner confused and wracked with guilt, accuses our protagonist to be a heretic and that he must be destroyed before he brings about a calamity to their temple. A battle ensues and the boy manages edge out his former friend long enough to make his escape. Thoughts in complete disarray, he runs and runs until he finds himself fallen on the ground in the middle of the dark woods almost blacking out from exhaustion. He pushes himself a little further to find an appropriate shelter and finds a seemingly derelict hut after walking around a little further. When he wakes up again, he finds himself greeted by the hut's owner - a girl of about his age that also bore the typical features of the lich's kin.
He spends a few days there gathering his thoughts and gets to know the girl and her isolated existence within the forest. She had been left here by her caretaker as she was told that her existence was a cursed one and that she should remain here to keep the everyone else safe. Wanting to help her and answers for his troubles, he convinces her to let him summon the lich through her. He does so and to his surprise, the girl's body reacts more strongly to the ritual than any other as he manages to summon the lich in a completely lucid state as opposed to the usual dreamy trance his possession usually entail. The lich is equally surprised to find himself in such a fitting vessel in so long and is cheery as can be about it.
The boy plays along with the lich's whims at first but eventually questions him on natures of their bodies that led to this event. As it turns out, the church of the lich have been eliminating people like the boy because they see it as heresy to be of his blood but also be unable to host the lich's spirit at all. The twist however is that they also eliminate people like the girl that allow the lich's consciousness to manifest properly since a sect within their church had decided that they should be ones to call the shots and they don't want to risk the lich ruining the doctrines they set for their own convenience. The boy is at a loss on what to do as this meant the church would absolutely hunt him down the moment his former comrade reports the crisis that they were in but the lich offers him a way out. So long as the pair agree to follow his instructions absolutely, he will guide them out of the mess they're in and save them from his own followers.