“The Highest Sky above,
the Inferno itself within.
The growling Hydra in front
and the Crown on my head.“
The palace of the mind is ruled by the Empress, the grown-up/awakened Dragongirl.
The Empress is able to tame/deal with the Hydra, which is the queen of Mind-Monsters, that represent (overwhelming) emotions and thoughts.
Humans often can’t deal with their strong emotions and they have a different way of handling these. Some people tend to suppress them, but a suppressed Hydra leads to an escalation of the situation: suppressed emotions add up and will (one day) erupt like a volcano. Therefore it is necessary to deals with the Hydra before she goes on the rampage and consumes the Empress/Mind-Palace.
Other people try ignoring the overwhelming emotions, but in the darkness grows nothing healthy.
The dragongirl is overwhelmed with the Hydra, but the Wingshifter helps her survive until she finds the Empress and learns to control the storm.
More about how the Dragongirl becomes the Empress and about the Mind-Monsters and the Hydra can be found here (The Origin of Nos).