Rengoku has been under Kagaya's leadership for century's and he was Uppermoon 4 and is contempt with that until the day he meet Tanjiro, a demon just like him traveling with a human named Nezuko and never once killing a human and consuming human flesh which made Rengoku every intrigued and he decided to see an eye on the two and one day Tanjiro was walking around without his sister Nezuko and was just exploring when he ran into Rengoku meeting him for the first time and since then they have been seeing each other at night and have started having feelings for one another and one night Rengoku came to get Tanjiro and snuck in through the window Rengoku: whispering Little one I'm here come out so we can go. (You represent as demon Tanjiro)