Shi ni Modori no Mahou Gakkou Seikatsu wo, Moto Koibito to Prologue kara (※Tadashi Koukando wa Zero)

Life seemed perfect for Oriana after she started dating Vincent in the winter of her fifth year at the academy. Little did she know, her beloved would soon die under suspicious circumstances. Before she can process anything, she wakes up to find herself back in her seven-year-old body with no idea how she died. When she finally returns to the magic academy in hopes of reuniting with her boyfriend, she finds out Vincent has no memory of her! Now she's back at square one. Can Oriana navigate this second chance at life and change the course of Vincent's fate? Making her crush work out really is a matter of life and death!
(Source: Cross Infinite World)