Emperor Varan didn't expect the Delarosas to have such a troublesome history.
Not only did they join the demons, but they also stole a piece of Furhengir's carcass, which the Black Rose Kingdom brought back from Gehenna at a great price!
It was no secret that Furhengir's carcass was robbed by numerous forces after it was brought back to the Black Rose Kingdom. That incident had always been a sore spot in the Black Rose Kingdom's history.
Now that the Black Rose Kingdom was on a fast rise and incomparably powerful to its past, it had become one of the few countries Emperor Varan least wanted to antagonize.
It was also for that reason that Emperor Varan chose to negotiate for true dragon blood instead of trying to seize it by force despite knowing how crucial it was for the Red Wyvern Ancestor's breakthrough and survival.