Since the outside isn't a place where you discuss what to do with a human amnesiac, Diavolo offers to go to the Demon Lord's Castle. The walk there is overall a pleasant one. You don't encounter any demons and the rural areas in the Devildom basically look like the ones in the human realm. The castle of course stands out with its height and architecture but you don't feel as off as you originally expected.
Having arrived inside, you are taken to a more private room.
"Sit down, (Y/N).", Diavolo points at the table in the center.
"And I will make some tea in the meantime. Do you have any preferences?", Barbatos asks.
"Just make me the same tea Diavolo wants."
The butler nods and leaves.
Diavolo sits down across from you. "And what is your first impression of the Devildom?"
"I sorta imagined things to be a bit more... grim and gloomy... But I guess this is way better than a literal hell. ...Eh, general question: Does it bother you that I am not all too formal? I started with a more casual tone and you didn't complain yet but when I think about it now, it does seem a bit inappropriate. I have never met royalty before..."
He shakes his head. "I personally don't mind. Do what you feel more comfortable with."
"Perfect. I will stay casual then~"
The door behind you opens up again and Barbatos enters with a tray of tea and sweets. "I prepared you Hellfire Rose Tea accompanied by Brutal Chiffon Cake. I hope it is up to your liking."
"Thank you."
Taking a sip of the tea and a bite of a cake you make a delighted face. If everything down here tastes as great as this then you certainly won't starve. "So delicious..."
Barbatos smiles. "I am glad to hear that."
Diavolo puts his cup down. "Tell me (Y/N), what if we don't find the cause of your amnesia? Would you prefer to stay here or do you want to be in the human realm?"
"Hm... Depends on what my life here would be."
"Due to your favorable timing, you could visit the local school, called RAD, without any major problems. You would live either with us here in the castle, with the future exchange students or with the demon brothers. What you want to do beyond that is up to you."
"And if I were to go to the human world, I would be all alone and lost?"
"Essentially, yes."
"...I think it is more reasonable to stay here then, if that is alright with you."
"Of course, even just having a human around is a good thing and if my current impression doesn't fool me, we will get along perfectly fine. You seem like a likable person.", the future king beams.
"And I believe Lucifer will be happy that he doesn't have to bother looking for the second human exchange student.", Barbatos adds.
"You did mention exchange students before... Who are they and why did I never hear of people going to the demon world for a student exchange program? I can't believe that such a thing can be kept secret for a long time..."
"That is because this is the very first time for a project like this to take place! To strengthen the bond of us demons with the other realms I decided to establish this project as the very first step towards it. During your stay here you will meet one other human and two angels."
"I- umm... okay. The goal sounds... nice." You take a moment to observe Diavolo's face that has 'enthusiasm' written all over it. "How could I disagree with someone as happy as him? Though it is reassuring that there are angels and a human here too."
"It must be a lot to take in for you. Since it's quite late already I would suggest that we do the formalities and details tomorrow and for the rest of today you may rest. Barbatos, would you show them their room?"
You stand up. "Thank you. Eh... Till tomorrow, I guess?"
He smiles gently. "Yes, have a good night and rest well."
"Please follow me." Barbatos keeps the door open and waits for you to walk through.
On your way to your room, you get to see a lot more of the castle. Luxurious furniture wherever you look and the sheer number of halls you walk through is overwhelming too.
"So... How long have you been working for Diavolo?"
"For a longer time than you could imagine. I take much pride in my work and- Ah, here we are. Everything you need is inside that room. Tomorrow I will come and pick you up at 8.", he hands you a small silver key.
"Alright... In case that that there will ever be something where I can help you, please tell me. I know it is your job but I still somehow get the desire to help when someone is so kind and hardworking."
"I will keep that in mind, thank you." He bids you goodbye and leaves you all to yourself.
You open the door in front of you. Just as everything else you have encountered in the castle so far; this room too is lavishly decorated. Changing into the clothes that laid on the bed, you notice that they fit you perfectly. "Scary how good they guessed my size... Demons sure are on a different level."
The bed embraces you like an old friend and it doesn't take long until you fall asleep.
I hope you enjoyed reading and stay healthy!