Astaroth

About
She is a demon who takes the form of a puppet. She is technically Arima Kouyou's familiar, though lovers is a more apt description. She is quite haughty and only seems to help out if it serves her or Arima's interests. If he dies, she will take his soul with her to hell so they can stay together.

She is one of the 4 grand dukes of hell and thus an unbelievably powerful magician. She states she could probably take care of most things, but will probably destroy more than they bargained for.

She confides in Shura that if Arima would ever be killed, she will kill everyone involved and maybe kill herself if she is up to it. She would not prefer to live Shura's life.

She first met Arima when he went to exorcise a girl she possessed. Instead of it just being a regular exorcism, he turned it into a sex battle which greatly piqued her interests. She lost and became his familiar.

Throughout the story she gives advice on various happening (Like Yura's possession) and she is even responsible for reviving and empowering (not intentionally) Kusanagi maru.

She was directly involved in dealing with Fenrir as she was the only one of the group who was able to grab the fairy ring and open Porenut. She had to possess Shura to get in the building though.

In the later chapters of the game, she is busy dealing with tectonic shifts in hell. It is revealed that Nero escaped as a result of the plan to create the Crystal Palace.

Trivia

 * Her name is a reference to Abrahamic mythology
 * Even her position is the same
 * Its name is in turn most likely based on Astoreth, a female goddess of fertility, love, sex and war.
 * The summoning ceremony performed by Arima is just something he likes to do, she can just pop in whenever she want.
 * She seems to prefer using lowborn/下賎 as an insult.
 * She refers to Kusanagi Maru this way as she is unbelievably annoyed by it's existence.
 * Deirdre is referred to as the Lowborn queen.
 * The insult itself might be a bit harsher than what lowborn might portray.