Echidna, the female monster, is Hell's Imperial Princess.
As the daughter of a royal family of hellions, she is entrusted with the punishment system for the human realm.
Her schedule is filled with bringing to justice those who've come to Hell for doing wrong.

One day, some unrighteous sufferers rebel against Echidna, and trap her in a masochist's bondage device for all to see.

"Laaadies and gentlemeennn!"