How the hell is a half pureblood in control of a pureblood's abilities?

idk if this is a spoiler but I'll just put it
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.He stole her dad's heart, he ate it making him a pure blood vampire

Isn’t he basically a half purblood

Hmmm.. I just got that information from another person.
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but this is just my theory. When blue hair dude was in a rampage, it was said vampires can have immense power if their desire is that big. We still don't know what his desire is all about, so that leads a question mark for that information. Second, I forgot what chapter but you can see our fl's dad heart was taken out, leaving the fl's wife shock. It's either blue hair dude ate it or destroyed the heart. This is just my theory but I think he ate it to become a full pure blood vampire. Knowing that, the mom decided to suicide with our blue hair dude. The mom hypnotize our fl in running away because obviously, she didn't want her daughter to get killed. The blue hair dude was supposed to kill our fl in her younger days but I think he was taken back. So I'm really excited for the upcoming chapters because we will soon find out what's that desire that made him betray the family that saved him.

This is my theory, don't assume its correct huhu(づ￣ ³￣)づ

I guess Hayan is mentally still weaker and therefore might be still influenced.