when a demon encounters a slayer, always only one of then walks out alive. But what would happen the one time they walk out together? In another world, tanjiro was turned into a demon, replacing nesuko. He is immune to the sun and only needs sleep to regain his energy. While nesuko became a demon slayer. however they were separated and tanjiro set out to find his sister alone, until he ran into muichiro, and they set out together. Will they always be enemies and are just working together for now? Or is there something more between them?