It was mentioned early that Betas don't inherit the crown. That's why he's not in line and his maternal family wants his younger half-brother dead. They plan to put that cousin on the throne instead, but it was revealed in MC's previous life that this cousin did not possess the blessings/power associated with the fairy king. The blood thing is because MC is a descendant of the fairy king and his blood holds power. With it, his maternal family can grow their power and the cousin can hold the throne.

I thought he was an omega did I read it wrong. ? Like I thought they took his blood because of it in the earlier chapters … maybe I need to re read