Both
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MazharShafiq
and IslamLife00 repeated exactly what I said in the last sentences of my paragraph :) One warning for the OP, you cannot do like typical female syndrome do and be an enabler. Non-Muslim women have earned the reward of the world for been an abuser enabler. Like frogs, they jump lily pad to lily pad. I am not saying your brother is evil and your victim, far be it. Your brother is a good person, he just need guidance and he is a victim too (because the parents are not doing their job). I am saying that this scenario could be repeated with a spouse WHO MAY BE AN ABUSER and you have been trained now in this condition to accept this abuse, you may repeat this with your real relationship. NOW HERE you are in trouble. If you allow your future husband to abuse you and you accept it, you are not a victim you ARE AN ENABLER. In Islam anyone who accept been abused goes to hellfire. There is no victimhood here allowed. No been weak and take it. There is no place for that in Islam. This goes for both sexes. If you are a woman get abused by another woman or a man and take it, YOU WILL BE THROWN IN HELLFIRE. If you are a man who get abused by another man or woman and take it, YOU WILL BE THROWN IN HELLFIRE.
That is right, you will be thrown in hellfire for been abused. So for the OP, take this as a training ground for your future. Learn now at this age to defend yourself and get your rights, CORRECTLY, because Allah is training you for the future. We are all been trained young for the future. I think, I know others may disagree, it is great that your brother slapped you. Allah made it easy for you and the person who slapped you is only 11. At this age he is soft and weak, no muscles (usually). Now the training begins...are you going to be victim, woes me, I am a female in distress, I am enabler and women are victim and men are wolves...mantra or scenario....OR.................................... ..
By the way, I don't think it is one sided. I believe the OP is at fault too. You also trained him like that. By the time he reached age 11 you had all the power to train him to respect you as an older sister. Where is your role on that?