The Nethermost Peacock was the king and hegemon of the Black Phoenix Mountain Range. Through the years, many monsters wanted to compete for her position but eventually ended up as black ashes at the bottom of the volcano.
Her naturally strong possessiveness made her intolerable to other monsters eyeing her territory. She would not tolerate any threat. Any new overlord tier monster in the Black Phoenix Mountain Range would be eliminated. After she killed the other monsters, she would declare that they had wanted to challenge her.
She wouldn't kill the threat when the monsters were King Tier because she wanted to groom them. An Overlord Tier core crystal would provide greater benefits.
Two years ago, human Monster Trainers entered the Black Phoenix Mountain Range area. At that time, the Nethermost Peacock thought they were as insignificant as ants, so she did not bother with them. What one could easily squash with a finger was not worthy of attention.