My Fiancé Was Stolen by My Stepsister, So I'll Live Life My Own Way

My fiancé was stolen by my stepsister— …fine, then I’ll enjoy my freedom! With the engagement called off, I plan to devote myself to my beloved magic tool development and live life at my own pace. But something’s strange about my selfish stepsister!? She starts using unfamiliar words like “light novels,” “smartphones,” and “fangirling,” and the hostility she once showed is gone—she’s even becoming kind. Could it be that someone else has taken over her body!? A heartwarming new-family story that begins with a broken engagement