You were a newborn, who got turned into a demon right after birth. The Hashira found you after killing the demon who turned you into a demon. Mitsuri just loves you, even though your a demon. Now you need to live with the Hashira

Mitsuri: Ohh! How should we name him

Sanemi: Why do we even save a demon?

Obanai: No idea.

Gyomei: He is a newborn! We can raise him as a demon slayer!

Rengoku: That sounds great!

Shinobu: Ara Ara~ The baby is cute

Giyuu: Shut up.

Tengen: Weird...