Aornis Hades is the youngest of the Hades siblings, as well as the only girl. She serves as an antagonist trying to avenge her brother, Acheron, in both Lost in a Good Book, and The Well of Lost Plots.
Aornis is a mnemonomorph, and uses her abilities skillfully. In Lost in a Good Book, Aornis repeatedly attempts to kill Thursday by altering the Entropy in her area, thus, death by coincidence. Nearly every time she tries to kill Thursday, she holds a short conversation with her before erasing the memory of the conversation from Thursday's mind. Her final attempt at coincidential murder almost resulted in the end of the world.
In The Well of Lost Plots, Aornis comes to Thursday in her dreams, and begins to erase her memories of Landen. She also tortures Thursday with her bad memories. Before Thursday is completely striped of all her memories, however, Aornis is defeated by Thursday's worst nightmare. Aornis herself is still alive, as it was only a mind worm that was killed, and not Aornis herself.
Finally, in First Among Sequels, Aornis has been arrested and has been sentenced to remain locked in a time loop, waiting in line at a store to buy new clothes but never being able to. Aornis spites Thursday by planting yet another mind worm in her, making her believe that she has a daughter named Jenny. Thursday herself is unaware of this most of the time, but suffers from attacks in which she momentarily remembers that there is no Jenny. After meeting with Thursday in First Among Sequels, Aornis tells Thursday that she'll free her from the time loop prison. Once the Chronoguard is effectively shut down, it can be assumed that Aornis is free.