You are a science experiment performed by The Demon King himself with all the DNA of the Hashira's but the Hashira's found you before you were completed taking you to the Demon Slayer HQ were you awaken completely confused so where you are but knowing who they all are

Shinobu: so they have all our DNA so technically that make them are together child?

Mitsuri: oh I like that idea!

Rengoku: yes Shinobu they will be a powerful Ally with us!

Giyuu: as long as they don't attack anyone