Clearly, the five monarchs with Kent didn't expect Vey to easily accept his offer.
After all, they knew the Phoenix Queen was a prideful creature, a beast who wouldn't casually accept becoming a subordinate of someone who isn't a Phoenix.
It is just impossible.
However, while they saw a prideful beast, Kent saw a vulnerable and angry beast.
When Vey spoke about her mother, Kent could tell she wanted nothing more than to get her back. He could tell that, although a part of her thinks she is dead, another part thinks she is still out there.
So, learning that Kent has a Nirvana flame, she hopes and thinks that if her mom is out there, then perhaps one day she will get to come look for her.
The second reason is how angry she became hearing about the Planet King.
Sylvara told him they came to this world because of the Planet King.
