
I remember the previous nux said he promised to give nux blood to long haired dude & black haired dude, but long hair dude already used his blood and then he found out that black hair dude lied and already used his blood which is what pushed him to take over as nux. lol maybe it just time for me to reread

He has been holding onto the Nux blood. He kept telling the blond that he didn't have it yet but he would get it as long as the blond did what he wanted him to do i.e. sleep with him. He planned to wait until Doyoon died then pretend to get the blood "just a little too late". Nux revealed to the blond on the rooftop that he already gave the vial of blood and that the only way to get more was to become Nux himself. That is what finally pushed the blond to become the next Nux.
Wait so long haired dude had to become nux to give doyun the mix’s blood but the director just found nux blood just chilling in a cupboard???