this are some spoiler read at your own risk... if you want i'm telling you!!! it's risky!!!
Yuki is the daughter of the Kuran family.
Kaname said that Yuki was the child born to become his wife.
In the Pureblood race, incest isnt uncommon.
Yuki was placed on a bed inside and she started to crave blood.
She looked older, maybe it was because of her vampire genes had returned causing her hair to be longer.
Kaname told her not to hold it (the craving) in, and she pushed him down on the bed and started sucking his blood and crying at the same time.
Kaname hugged her and told her that He held on to an anxious emotion, waiting for this day.
Yuki remembered her parents and became confused. Kaname hugged her from behind and calmed her down.
Yuki said that it is abnormal for her to like Kaname, her own brother.
But Kaname replied, "So? We are bethrothed"
You find out that their parents are also brothers and sisters.
i got this from a vk forum
so thank you 
