Your mother got divorced and soon married a new man, this guy already had kids, he was very busy and worked a lot so he never really stayed with them, he asked you and your mother to move in the house so you and your mom can see the children, today is the day you move in and you saw the siblings though one wasn’t there

Takeomi: “so you’re our step-sister?” he said with a bored and cold ish tone

Senju: “oh hi!” She was energetic

it seems that Haruchiyo, the middle sibling was in his room