Ju-On: White Ghost sounds like the standard "family torn apart by savage murders, their souls are now restless" conceit of the series, but Ju-On: Black Ghost...well, it's perhaps best that you read the official description. From Bloody Disgusting:
"Nurse Yuko (Ai Kago) is left in charge of a young girl named Fukie, and begins to experience strange things. Medical examination reveals that there is a 'cyst' in Fukie's body. The hatred of the unborn one is feeding off of the young girl, and curses the people around her. This is the grudge of someone that could not be born... Filled with an unimaginable 'hatred', people are killed one after the other with a curse. "
Er... what? I take that to mean that Fukie had the rare medical abnormality in which a pair of twins are conceived, but one is absorbed very early on by the other in the womb. Why, then, is the absorbed fetus so angry? Hell, not only is it angry, but the unconscious mass is "filled with an unimaginable hatred". Sorry, but no, it's not. It never even had a brain, it's a non-functioning lump of unformed tissue. Lumps of tissue don't have emotions and they certainly don't hold grudges.
I'm all for coming up with original twists to tired franchises, but this is just silly. The whole foundation of the Ju-On series is that when something truly tragic, like the savage murder of an entire family, happens, the act is so powerful that the spirit of the victim remains to curse those that dare disrespect it again. It's not like we're talking about an abortion here, which would be an interesting twist on the birth of grudges, we're talking about a completely motiveless process of nature. A fetus being absorbed before it can even develop does not qualify as a savage act. It's not even an act, it's simple biology.