Koi Is My Sister, but I've Been Open-Mouthed

I am the crow's mouth, saying that so and so is unlucky. She is a koi and all her wishes come true. The system insists on tying us together - if I'm unlucky, she will suffer, if she's lucky, I'll take advantage. My sister said to me: If you dare to talk nonsense, I will kill you. I said: Sister, isn't your wish coming true? She smiled: Yes, so you'd better be good. Later I discovered that the crow's mouth would become good as long as it was said to protect her. But the system said that if you want to unbind, you can, but the condition is that we really love each other. We both looked at each other: Can we change the conditions? System: No. My sister: Then shut up. Me: ... Okay sister.