Ore no Yancha na Otouto ga Shiranai Oji-san ni Kawareteiru

"Oh, did you find out I'm a sugar daddy? See, I'm a hottie, you know? I'm cuter than the girls around here, so I can make more money. Well, it doesn't really matter to you, bro, right?" My little brother is being kept by a strange old man. He receives money from his "daddy" and has relationships with multiple older men. He's a troublemaker, a bitch, and loves sex. "Hey, bro. You were secretly watching me having sex with that old man, weren't you...? Was i cute back then? Do you want to do it with me, bro?" Will I tell him to live an honest life? Or will I join him in his downfall...