Kimi wo Sukuu Tatta Hitotsu no Houhou

On that day when my beloved idol was stabbed in front of my eyes, my life-long time leap began. Nodoka is working hard on her former classmate's idol, Akki. One day, she encounters a man and a woman in a back alley - but that man is Akki! Stabbed and covered in blood, Akki hands her something, and the next thing she knows, she finds herself back in high school! If I change the past, can I change the future when Akki gets stabbed? If so...What is the future they will reach after the time leap?