男が滅んだ世界 ―英雄戦士のハーレムワールド―

Aragaki Kuuya was involved in a maritime accident when he was 8 years old and was transported to another world. That other world, which at first glance seemed peaceful, was actually a world where the countdown to destruction had just begun. It was a world where men suddenly transformed into monsters called Renma! Kuya is at a loss when his master, who guided and raised him as a child, finally turns into a demon. Then, a ship carrying a young girl drifts ashore from a neighboring continent—!? The last man left in the world can change a world on the brink of destruction! (Source: Takeshobo, translated)