My Sister wants me Dead - I'm a Demon on a Path of Revenge!

After being held captive, being abused and experimented on for over a century by her foster family, the young demon Lily, finally escapes after killing the patriarch. Wounded she flees the place of her upbringing and returns to her homeworld, Tiadar. There she meets a Death Spirit who tags along on her flight but who has his own motivations for sticking to her. Death itself has a special interest in her.
With this grotesque creature by her side that she grows weirdly attached to as their joined travel continues, Lily has to finish what she's begun.
Her vengeful foster sister finally catches up to her and Lily has to confront her one more time. Both of them seek revenge for what the other has done to them. But who will gain it in the end?