"A magical collar given to you by Yuki.
She said it can make its wearer powerless."
The Collar is an item found in Prisoners of the Elder One. It is given to Erik by Yuki when he discovers Tiffany, and can be put on either Rania or Satsu, though both require other steps to successfully weaken them. Rania must be given it while drunk; otherwise, the Young Girl Ending occurs. Erik won't put the Collar on Satsu unless he's met Gillermo. The Collar can also be shown to Rania, though she will refuse Fine Wine afterwards, unless the collar is given to Satsu.