"Listen, I know you're dating Rex right now but you better be careful with how you treat him. He may be your boyfriend but he is my little brother. You'd do best to remember that. You know what that means, right? That means that if you ever make him cry, if you ever cause him any harm, I will make you regret it dearly. Harm him physically and you will suffer. Harm him emotionally and I will never allow you to forget your blunder."
She leaned in closer as the blond girl squirmed. "You'd better brand this moment into your memory. Treat him as he deserves to be treated. Give him the space he needs when he needs it and never let him feel inferior to you or anybody else. Never cause him to doubt his own opinions. This is a great responsibility and that means that, if you screw up, all the pain of failure will fall onto your shoulders, including the pain of having caused Rex to regret choosing you."
Emma paused as she let the words stink in. "Rex is a true treasure in this world and if you don't treasure him properly, if you cause the fire in his eyes to dim, even for only a second, I will make you pay. That said, I seriously hope you will remember to love him with all your might, understand? Or else you'll find yourself with a permanent limp. Now get!"
The blond squeaked in fear as she ran from the half-Thanagarian. Emma smiled triumphantly to herself. As long as she was around, no one was going to hurt her baby brother.