Demon Slayer: You Promised to Protect Me, Yet You Left First

The protagonist doesn't transmigrate and doesn't know the plot. Some parts of the original story have been changed, and a few new characters have been added.

Born with clear, well-defined marks, but unable to learn a Breathing Style yet (it takes time), so he can't become Muzan's father.

The early developments are similar to the original, but some parts will change. The eldest brother will get a chance to make up for his regrets.

Since new characters have been added, the demons' combat strength will be raised accordingly, and new demons will appear as well.