Lanling did not really want to kill the Blue Demon Lord, because someone as noble and shameless as him could be very useful at certain times.
However, he had to kill him because Lanling needed his head to intimidate the Rakshasa King, and just the head of the Blood Demon Lord alone was not weighty enough.
Most of the other members of the Blue Demon Clan were dead, and even those who hadn't died would soon be devoured by the Mirror Demon King and become zombies.
Thus, following the demise of the Demon Sky Clan and the Blood Demon Clan, the Blue Demon Clan was also wiped out, leaving only nine of the Thirteen Demon Flags loyal to the Rakshasa Tribe.
Lanling raised his knife several times, but each time he did not kill Princess Beili.
Of course, it wasn't because he couldn't bring himself to do it; this woman had committed heinous crimes, and killing her ten times over would not be enough. But someone like her could indeed be quite useful in the future.
