what if hanako and tsukasa has a sister which they hid from everyone but one day there sister came what will happen to find out read

Y/n Amane and Tsukasa's younger/little sister. They meet in an unusual way and what happens next is what you will find out. Y/n is a new rumor that her rumor changes by the day, her brothers don't remember her at first, but then start to regain the memories they've had together. She's quite powerful and smart, but don't test her. (will edit this and I'm still working on the cover page btw)