Rengoku/Senjuro

Rengoku's little brother Senjuro was with him on the Mugen train arc and he was on a mission with Tanjiro inosuke and zenitsu to fight demons until the train demon head was cut off by Tanjiro using cyrokomidamo and until the train tipped over trapping all the passengers but no one was harmed and without injuries so Rengoku helped Tanjiro close the wound until upper moon 3 Akaza arrived and they started fighting but things took a dark turn ending with Rengoku's death in Senjuro's arms