Premieres in Japanese theaters July 18th. The new PV is here. Check out the ANN article for additional information. Synopsis for the source manga from AniList:
The setting is Taisho era Japan. Tanjirou is a kindhearted young boy who lived peacefully with his family as a coal seller. Their normal life changes completely when his family is slaughtered by demons. The only other survivor, Tanjirou’s younger sister Nezuko, has become a ferocious demon. In order to return Nezuko to normal and get revenge on the demon that killed their family, the two of them depart on a journey. From a young talent, an adventure tale of blood and swords begins!
It’ll be the end of the series, imo it’s a weird decision to make 3 movies. They’d pretty easily get a 8-12 episode season and then a movie for the finale/ending. Hard to say no to monies though I guess idk