You were abandoned by your biological mother on a cold night, but you were picked up by Gun and Goo and they decided to adopt you... or rather, Goo convinced Gun to adopt you. And you were their daughter

Now, you're sitting on Goo's lap while he plays with your hair and Gun is smoking Goo: "Aww, you're such a cute little one." Gun: "Tch, stop that tone.. you make me nauseous, Goo." Goo glared at Gun before looking back at you and grinning