I think and what i've read.. isaac hesitated biting yuki or push to the limit of what he can sips of blood from him to make yuki become his kin thats why he died of his illness. I think its a hint that he can actually make it possible that haru will live with him forever. Well.. thats what i understood from the way isaac said to haru. Im hopping for that promise of forever was literal for them.
BLOOD LINK SPOILERS
Similar to Blood Link, I think the vampire can convert their target into one of their own. He asked if he chooses his family or him, which would mean RIP family cuz he immortal now
I can't. I feel sad thinking haru will die someday and Master will be alone again ⊙︿⊙ is there any way they can make haru immortal? I know the story has ended, but I still feel sad knowing that he will die of old age someday (ToT)