User blog comment:Xilinoc/Ch. 543 - Letters/@comment-2211792-20130626143149/@comment-11051098-20130627073358

Masaki and Ryûken were to be married once, I doubt they would be related (makind Ichigo and Uryû cousins). Masaki did call Ryûken's mother aunt, but it might have been a cover because they didn't want to reveal the upcoming marriage at the time.

Masaki was a Kurosaki, Ryûken was an Ishida. To my knowing, 2 different and unrelated Quincy families. Well, related to some point as Yhwach created the Quincy and all of them apparently are of his blood, but still.