Maria's childhood friend Takumi apparently has a dark secret: he and his family are protectors of the Maria family, which includes the immortal grandfather of Maria, who has a secret lair in the basement of their mansion. The immortal Maria wants Bloody Mary to be brought to him, because he believes the red-haired vampire is the one who killed his son. But despite Maria's hatred of vampires, he's still quite attached to Mary.
It's weird when elements of a manga are very similar to elements in other manga, but with completely different plots. Or do they? My favorite manga of all time, Loveless, also has an older man with long blond hair who has a younger (looking) companion with cat ears, and though the cat-eared character seems like they are being coerced into this relationship, they are the ones with the real power. Because the relationship between Maria and Mary reminds of that other manga, I find I like this maybe more than I should. I'm still not quite sure about the one female character and her role. The flashbacks to Maria's childhood with Takumi revealed how he discovered that his cross would grow into a huge thing he could use to stab vamps with when he bled on it, which was a pretty cool twist and hopefully will turn out to be important in Maria discovering how to do exorcisms.