OMG the horse is way too in front of the cart. I have no clue how old you are but IMO bedrooms are place for rest so maybe keep the toys out of there . Buying a house is complicatd enough without looking only for bedrooms that suit your stuff. Find a house that is right in all the important areas like kitchen, living space etc then come back here with the bedroom plan and you will get help.

You won't get a lot of support for theme master bedrooms here. You might want to post on the Reddit page for your specific interests to ask for ideas.

Once you get in the house and post a pic of the room with the existing items that you want to use people will be better able to help you make choices.

I don't know what a Death Note is but it sounds moody. If you want you can search "Green and Black Bedroom" (for instance) here on Houzz and get inspo pics. It sounds like a Charcoal or Navy wall with Teal and Blue Velvet is in your future lol. Good luck with the house hunting.

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It really makes sense to get the home first. What if the bedroom is really small but the living room has a great reading nook? What if there is a huge set of windows in the bedroom that you want to sit by, or no overhead lighting, or each wall has a closet or doorway on it? Have fun daydreaming for now and when you find you place come back here with pics and you will get lots of reaponses. Hope the housing hunt goes well.

Click on this site and you will find so many rooms, it will give you an idea of what you might like to have. https://www.houzz.com/photos/query/teal-and-green-bedroom-with/nqrwns

Themes are for events, not rooms. Never for rooms.