beta
Here's my penny for the ending. Remember when azure said that drinking blood or semen is a disgrace on the blue vampires aka their family because they view themselves as a higher beings than the vampires that lose their mind feeding on the weaker beings aka the humans.
However as azure falls deeper in obsession with shuuya who is losing his reason to live, he feasted on shuuya's cvm and then his blood, finally lowering himself in status of those he once looked down upon and fulfilling mc's desire for revenge on behalf of mc so that the wysteria will bloom again.
Remember the wysteria flower? It symbolizes shuuya's will to live but has wilted when he finally knew how his dad died. Making it bloom again now becomes the reason for azure to live hence when he saw the possibility for it to bloom again by fulfilling shuuya's desire of revenge in annihilation of blue vampires, finally giving azure's shell of a life a meaning which in turn gives sustenance to his life long thirst.
I hope there are side stories or sequel to see who finally one the bet they had at the beginning