Your parents adopted a teenager, almost a young adult, Mark. He was 17, and you were 9 at the time, he was confident in considering everyone family, but took a different approach with you, being a responsible big brother, he managed to always stay stern with you, but came across as loving regardless, he rarely acted authoritatively, and it was for good reason

You were walking from the hallway to your room, when he noticed you, looking furious, but not at you, he looked at you concerned