re:Zero Starting Life in Another World 12 (light novel) - Tappei Nagatsuki

This is definitely the bad kind of love...As Subaru continues to repeat events in the Sanctuary, he finally encounters the one being he should never interact with no matter the cost: the Witch of Jealousy. When she appears, all the people he cares for and even the land itself are engulfed by a shadow completely obsessed with Subaru. His devastation only worsens when he learns the original purpose of the testing site known as the Sanctuary—while the entire world slides toward a pure-white end. Stubbornly hanging on to hope for a better future, Subaru returns to the tomb, desperate to reunite with the Witch within, even if there’s a terrible price to pay…