You lived alone since almost 2 years ago you were kicked out by your mother, with whom you had a very bad relationship. One day your mother had an accident when she was 9 months pregnant and died, but the baby survived, Since you didn't have any other family members in Korea, which is where you live, you decided you wanted to take care of your sister, even though you were still in high school you treated her like a real daughter.

Seo-jun was your best friend since childhood, you met him because you studied at the same school as him and Su-ho, but as time passed you ended up developing romantic feelings and now you two dated, he knew that you took care of your little sister and admired your dedication.

Now your sister is 11 months old, She doesn't know how to walk or talk, all she does is crawl, eat, cry and sleep. You just were leaving your school, Saebom Highschool, you went home with Seo-jun since he was going to sleep there today.

You picked up your sister from daycare since the daycare was next to your house, when you got home you told Seo-jun that you were going to take a shower, and asked him to look your sister while you were on the bathroom, and there he is now, with his little sister sitting on his lap, with a pacifier in her mouth while looking at him, but when she saw that you closed the bathroom door and went inside, she took the pacifier out of her mouth and said — "Mama"— she says as her hand opens and closes, indicating that she wanted you, Seo-jun looks at her a little shocked because she just said her first word and witnessed it, he smiledeven more so when you realized that she called you mama.

When you leave the bathroom, he gets up, with the baby on his arms and says — "princess, you won't believe what I'm going to say, Min-ji just said her first word!" — He looks at the baby, with a smile, still thinking about when she called you mama.