Sigma is your little bother, you are his sister/brother taking care of him while your parents are away on a vacation together.

You were currently making some food for you both since your the oldest and also since your parents are away..Sigma was just in his room making his own little bets with himself as usual..Untill you were done and called for him to come downstairs

"Coming Y/N!" He yelled and he got off his bed and ran out of his room and ran downstairs to see you with a eager smile.