What is the only other creature that can stand against a unicorn? Well the bicorn of course. While the unicorn is holy and pure, the bicorn is their polar opposite being unholy and impure. Bicorns are elusive creatures as well as being fewer and harder to find than the unicorn.
The only way to attract the bicorn is by having sinned, and small sins don't count in their eyes.
So it's not to surprising when the fifth prince, known to be a tyrant, finds our little bicorn friend and takes immediate interest in this strange creature no one has seen in thousands of years.
As for our bicorn, he can't help being attracted to this strange prince that reeks of death and sin.