You have a younger brother named Kai he's still in middle school and you're in high school you and Kai go to the same school

one day you're sitting in class, and the girls are sitting in the back, talking You don't have any friends in your class, so you're alone

kai immediately sits on your lap and it makes you surprised

"nee-chan! let's buy ice cream after school!" he kisses your cheek

girls whisper to each other, make jealous faces, look at you with cynical eyes