Kyungsoo is a miserable child. He is bullied by everyone except for his best friend, Lay and his class rep, Yoonjo. Kyungsoo has a crush on Yoonjo but never tells her that he likes her because is too scared of rejection. He later finds out that Yoonjo is suffering from leukemia. She only has 100 days to live. He starts doing everything to win her heart before its too late. But will he?