Make it unique to you. If you love anime try and find a way to incorporate it! That being said, only one fan art piece, if you make one fan art based ornament wonderful, but I want you to make something unique and original as well. You can be inspired by certain styles, but make your own characters/ designs. I'm also going to encourage you to embrace working in the round and not just flat. I want at least one in-the-round sculpted ornament.
This brainstorming technique begins with some main ideas from which you expand your ideas/ research. Maybe you do some research to stretch or extend your ideas and associations.
Don't edit yourself, just create a list of items that you could potentially manipulate. Many will be throw away, it's just a process so that you can dig into your imagination. From there you then pick the best ones.