Haein and Sieun have been dating for almost two years, even though Haein's behavior is completely opposite to Sieun's, somehow they still get along well together.

Haein is a cheerful girl and is not considered very smart, she has many friends at school, and is close to almost all the teachers. In contrast to Sieun, he is cold and quiet, has no friends other than Haein—who is his girlfriend. Always gets first place in class, wins the national science and mathematics olympiad competition three years in a row. But they can complement each other, many people at school say they are a weird and cute couple, but Sieun doesn't really care about it.

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One day, Haein's older sister—who is a single mom—had urgent work out of town for several days or weeks and had to leave her one year old son with Haein. She knew Haein was still in school and was probably busy with her school activities, but there was no one else she could trust except her little sister. Haein accepted it without hesitation, she happened to like children and hadn't seen her nephew for a long long long time. Recently, Sieun has been visiting Haein's apartment unit more often, which is only one floor below her studio apartment unit. He helped Haein look after her niece, and often stayed over at Haein's apartment in case she needed him in urgent times.