It could be that your brother obtained some compromising material related to porn and exploited it to blackmail you. Maybe he's trying to get something from you or control your actions.
Little girl comic porn is a deeply troubling issue. It violates the rights and dignity of children and can have long-lasting negative impacts on their lives. Laws exist to prevent and punish those involved in creating, distributing, or consuming such harmful material.
It might also be a term of endearment for a younger male friend or acquaintance. In some groups, people use 'brother' in a friendly way, and 'little brother' could be a specific person within that group who is no longer interested in stories.
There's not enough information to say exactly who the little brother is. He could be an ordinary boy in a family who is the youngest among his siblings.