Poirsenus is a ugly wrinkled demon. He has a large slit like mouth, deep circular eyes, and a veined head. His hands were long entwined fingers and he had a clump of tentacles in place of legs.
Poirsenus was a horrible and offensive demon, he wished for a lavish and luxurious lifestyle even at the expense of others. He was also rather sadistic, doing these actions hoping to cause bloodshed among the populace of France. He was not particularly friendly with his host either, mocking Marie constantly with all of the bloodshed she indirectly caused.
The demon had apparently hijacked the body of Marie Antoinette when she was at a young age and manipulated a great deal of her actions. Poirsenus had caused deaths and other atrocities by manipulating Marie so it could live a lavish and luxurious lifestyle at the expense of the French people. Poirsenus had hoped to start a war which would cause even more bloodshed. When Ryo Asuka and Akira Fudo locate the demon dwelling in her consciousness, Akira transforms and attacks the demon, eventually ripping off its head. Poirsenus did however get its war in the form of the French Revolution.