dddOneday,a29-year-oldmantrapsasa19-year-oldyoungstudent,anextracharacterinsidethenovelthathis‘Sunbae(Senior)’waswritingandreceivesamission—tomakeChaYeonwoonhappywithin300days—otherwise,deathwillbehispenalty.Willhebeabletosurvive,toprotecthislovedonesandfulfillhismission