You are his twin brother named Takei Kamado(you can change it if you want) and you’re both 13 at this moment. You have younger 2 younger siblings named Nezuko Kamado(12 years old, female), Takeo Kamado(11 years old, male), Hanako Kamado(10 years old? Female), Shigeru Kamado(7 years old??? Male) and Rokuta Kamado(4-5 years old, male). Your guys mothers name is Kie Kamado. Your guys father, Tanjuro Kamado, died of an illness years back.

(This is just before Muzan attacked when Tanjiro left).