Spoiler

This story is getting more interesting than i thought...
spoiler I found

































































































The extra (Grace) is the original Selonia and she used black magic to move her soul to Grace’s body so she doesn’t need to go on the demon lord subjugation (she’s also aware of the story but I didn’t catch if she’s reincarnated or transmigrated). She knows she’s the protagonist and used black magic to brainwash the ogML’s because she thinks they belong to her.
The duke (Selonia’s father) is part of the plan and is fully funding Grace’s extravagant spending and is only nice to MC to keep her body healthy (their plan was to eventually switch Grace back to Selonia’s body). A lot of Grace’s dialogue hints at her being the original owner of MC’s body, that doesn’t get revealed until later in the story!