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Just in case this is a serious post, here is a serious answer. Unironically, introduce him to lifting. He is 16, it's literally the best age to start, and everyone who does it correctly ends up loving it. It will also help dilute the onions inside your brother. It might not get him completely unhooked from vtubers, but it will give him a new outlet and maybe even a new, actually healthy obsession. Trust me, nobody ever regretted being jacked in high school.