Ao no Yami Gin no Yume

Krusnik Keep has been hunting his vampire for 300 years. Wishing to end it once and for all, he kills his vampire and watches him turn to ash. But he discovers all has not gone to plan, when he returns home to find he is still immortal and can sense the lingering presence of his vampire. What has happened, and what role does it play in the lives of former familiar Soosa and the Krusnik of his once master, the vampire Endless? Fraught emotions are brought to the fore while ghosts need to be laid to their final rest...

(Source: eManga)