User blog comment:B214/Volume 23 discussion blog/@comment-188.241.89.129-20170510202700/@comment-31137559-20170510212453

We don't know. Most likely cousins. It's the same way we don't know how Bedeze Abaddon and Kuisha Abaddon are related. Neither do we know how Falbium Asmodeus and Zephrydor are related. All we know is that they're from the same family. And you said that you're writing a fanfic, so just come up with something. Basically all DxD fanfics have info that is made up by the one who wrote it. No one's going to get mad at you getting their relation wrong. Again, they're most likely cousins or he could be her uncle. And he probably left the clan before Tsubaki was even born.