Rookie boygroup Infinite was appearing in a show called “You are my Oppa” airing on Mnet, just before their debut.
Infinite was given a little sister by Epik High Tablo (who acted like their mentor) who stayed with them at their dorm. The purpose of having this little sister was simply to make Infinite realize that the soonest they debut they will have fangirls all over Korea, so Tablo wants them to learn about how to treat them well and consider them like your own little sister and not only as fans.
It was hard, as their “little sister” was not easy to be pleased. There’s this one scene in their early episode where the boys tried to impressed their little sister with their dance moves. Known for their super sync dance moves, this scene shows their dance skills to the audience as well.