"Kim Jongin is the regular boy-next-door, with the burdens only a teen should be allowed to carry."

That was a made-up joke. 

Kim Jongin is not the regular boy-next-door because he doesn't have the burdens only a teen should be allowed to carry. He has to take care of his younger sister, 15-year-old Kim Jimin, and has to juggle between solving teen girl issues and doing his part-time job as a tennis instructor--and he's only good at tennis. 

Then a girl bikes over his foot and nearly sends him into the hospital for possible toe fractures, but instead sends him into further chaos, and further into a new dimension called love.