Character titles would be trademarks, not copyright.
However the specific art you create of a character is copyrighted to you. You created the work, it's your copyright. However using someone elses freely available art is arguable under fair use. It's improtant to note that YouTube largely blindly obeys DMCA complaints because they face legal issues if they don't follow them but it's the complainers legal issue if the claim is false. By blindly obeying Youtube is absolved of most legal involvement.