AccendereDark
The mages of the Demon King's castle conduct a magic experiment that will allow them to beings from other worlds. The experiment is a success... except that they randomly summoned a redheaded human.
And the demons imprisoned the human in a cell right next to the one that is going to be inhabited by the captive Princess.
In all honesty, life in the cell was a little better than back in Cale Henituse's old world. Although he was still guarded and couldn't risk having to act like a spoiled trash in front of demons that could kill him, it was still relieving that he didn't have to continue that trashy facade. Despite being demons, they didn't torture him for information or anything and even provide him with three meals a day. Living in a cell was a bit unpleasant, but the fact that they even provided him with basic necessities was a lot better than nothing.
But it was so damn boring. At least give him something to read!
Soon, though... Life in the Demon King's Castle turned out to be one hell of a chaotic mess, especially when the captive Princess proceeds to drag him into various adventures during their stay in the Demon Castle.