The protagonist, Nagisa Rokudo, once died and was reincarnated. It wasn’t a different world reincarnation or a modern fantasy reincarnation, but a place that closely resembled the world he originally lived in. Although there was a slight disappointment, Nagisa had a childhood friend in this world. She was cute, beautiful, smart—a perfect childhood friend. However, she fell ill and couldn’t move her body properly. But by some stroke of luck, a miracle happened, and the childhood friend recovered and became lively again. And—quietly and unnoticed—she had transformed into a yandere who harbored a demon within her.