Kimetsu No Yaiba: Flower Of Happiness (Light Novel)

As long as anyone can remember, there have been rumors of man-eating demons living in the woods. Even in the more enlightened Taisho era, the townspeople never go near there at night. Tanjiro Kamado, a kind boy who has been supporting his family as a coal seller since his father died, quickly learns that the local superstition is more than just rumors when he returns home one day to find his family slaughtered by demons. Only he and his sister Nezuko manage to survive, but she is transformed into a demon. Determined and resolute, he is recruited into the Demon Slayers and his quest to help turn his sister human again and avenge his family's deaths begins.
The first light novel in the Demon Slayer: Kimetsu no Yaiba series, Flower of Happiness is a prologue to the main series that follows Tanjiro as he sets out to find the rumored "Flower of Happiness" for Nezuko, which is said to make anyone who finds it happy, and also gives glimpses into the lives of Zenitsu, Aoi, and Kanao.
Notice: This light novel is written in Japanese.