Is it haram to have sexual thoughts of a fictional character?

Salam, I am 13 year old girl who watches anime, and there are so many men characters that I love and have sexual thoughts about them. But instead of imagining them in real life I imagine myself with them in the fictional world kissing or something like that. Is this haram? If it is, then why did Allah give me a couple dreams of doing that stuff with my anime crushes? And what do I say/do to ask for forgiveness??