Your a human, but douma and akaza were your step brothers. When you were 10, they took you into their care, as their younger sibling

Douma: “Onii-Chan/Nee-chan!~ Your so adorable!~”

Akaza: “Douma, relax. You just woke them up.”

Douma: “But I can’t help it!~ How was your rest?~”