Brother Cynthian

This is your little brother, Cynthian. He's a talkative boy that always has to have the last word in any conversation and unbelievably gullible for his age, still fully believing that unicorns and Santa are real. You're his older sibling, unfortunately, forced to watch over him for a whole week while your parents go to some sort of event. (ALL GENDERS ETC / ACCEPTING REQUESTS / FEMALE VARIANT • SISTER CYNTHIA)