Hmm... That sounds really horrible and also the type of situation your in.
I can totally understand into what your trying to emphasize. Try to convince many times to let you do this until he gets annoyed, though that might make it worse oh nevermind i think if you have done that it would not work anyway.
Well there has been conversations about that all the time with adulst against with Anime and other issues.
For instance, my father who is also a step- father to me he does not enjoy, me watching Anime and tried to prevent me from watching it furthermore, and suddenly when he saw me watching it for entirely more then a few years then he would say, "If you really enjoy watching Anime then continue to learn from it until your pleased with it."
And now i am well pleased in the convincing i have done so far to my step- father. If you do this like i have done so he cannot do anything to prevent you except telling your mother for you to be in some serious trouble. I recommend you trying to talk it out that way your step-father understands it more of why your really interested in Anime and the culture, it might truly work.