Simi's real name is Xiamara (after her mother), but everyone calls her Simi (Charonte for "baby"). She is bound to Acheron, who views her as his daughter. When one of Acheron's mother's Charonte demons gave her to him to care for, she was three thousand years old, the equivalent of three human years. She can also turn into a multi-colored dragon tattoo and reside on Acheron's body. In her demon form she has red and white marbled skin like her mother.
Artemis calls Simi 'It' and Simi calls her "heifer goddess." Artemis is jealous of Acheron's love for the demon and Simi resents Artemis' abuse of Acheron. She calls him her "Akri," which is Charonte for "master," but she is not subservient to him. Simi talks in the third person, referring to herself as "the Simi."
Simi unwittingly causes a lot of trouble. She loves to eat everything, so Acheron often has to tell her not to eat people. She follows instructions literally, such as when Acheron told her to take care of Tory. He meant that for one afternoon only, but didn't specify a time frame, so Simi watched out for Tory her whole life. The most devastating occurence was when Simi had sex with Nick, who didn't know who she really was. Acheron was furious with Nick and cursed him, which set into motion a series of terrible events.