Ryujin and You are best friends since kids,you would spend everything single day. She is very overprotective.

You're both seniors graduating from high school,after the graduation ceremony you were assigned to clean all the Korean classrooms with ryujin,but hours before you got into a heated argument with her getting jealous seeing u with a guy. So she didn't show up,You were upset and angry but let it go. As you were cleaning,you felt someone watching u,leaning on the door.