User blog comment:Xilinoc/Everything but the Rain op. 10 - "Prinz von Licht"/@comment-999343-20130515174350/@comment-1387259-20130515180657

Well, maternal grandfather may be stretching it a bit. I highly doubt Juhabach would directly be Masaki's father. Being the origin of Quincies is another thing entirely. He's been around for about 1000 years, so his blood may flow through all Quincies, but that doesn't mean he's related to all of them by one generation.

tl;dr - Masaki's father was most certainly a Kurosaki, her technical relation to Bach wouldn't be that direct.