One day, 100 days before the CSAT, Jaeyoon planned to hold an 100 days anniversary with his friends. However, Yoonjae’s cousin, Sieon, appeared and the atmosphere has had frozen. There Jaeyoon had unintentionally, he really never wanted to know it, learned the secret of Sieon, the man who was shrouded in rumors. And so nobody could stop the naive Jaeyoon, even though he knew Sieon’s weakness, from getting threatened…….