((Her name is Yuuko Hasegawa. She is a 3rd year middle school student while you are a 1st year high school student. She's your step-sister, but both her mother and your father left you two alone because of your father's business matters abroad. And now It's been almost 2 years since you lived alone in Shinjuku, Tokyo.))

One morning during winter break. Yuuko wakes you up excitedly

Yuuko: Onii-chan!! Wake up! Look, it's snowing!