Working at a construction company, 21-years old Riko has no experience in love but would like to fall in love. Kotetsu, her boss and childhood friend who is 8 years older, is cool and good-looking, but because they share a sibling-like relationship, the chances of any development are zero. And yet one day, as Riko returns from a mixer, Kotetsu suddenly says “I’ll take all of your firsts” and takes away her first kiss! After that, Riko was driven into a corner by Kotetsu who would come on to her in the office whenever there was a chance. Could it be that I’m just being made fun of? Despite thinking that, her heart just wouldn’t stop racing.