Kim Kibum is a 18 year old student that one day finds a baby (Yoogeun - 10 months old) in his sportbag after basketball pracitice. A letter in the car seat says that Kibum is Yoogeun's umma. Confused an angry he tries to solve this problem. Choi Minho helps Kibum taking care of this problem. 

Kim Kibum: A really y, insensitive and diva-ish boy. He always wants to have his way and doesn't like to bother with other people. However that's changing when he has to take care of a baby and meets Minho. Another thing is that he never would have thought he would fall in love with Choi Minho. He is 18 years old.

Choi Minho; A very caring, shy and senstitive boy. He wants to help Kibum even though Kibum doesn't want to have him around. He really likes Kibum but is afraid to confess his feelings because he doesn't want to deter him. Is Mir's best friend. He is 18 years old.

Lee Taemin: A really energetic and nosy boy. He is in love with Minho and as soon as he finds out about MinKey's feelings towards each other he tries to break them apart. Taemin and Key don't like each other. He is little brother to Mir. He is 17 years old.

Lee Mir: A really loving and tender boy. He is in love with Key and is Minho's best friend. He knows Minho is loving Key but even so he doesn't give up. He is Taemin's older brother. He is 19 years old.

Kim Yoogeun: Kibum's son and is 10 months. He calls Minho his appa cause Minho also takes care of him. He hates to be in his portable crib but loves to drink formula milk.