Yeon Iseul, the #1 student in school, suddenly gains the ability to see people's true feelings as 'hashtags.' But when she sees her first love, Sung Shinwoo, he attaches a tag to her “#UsedToBeFirstLove_Trash”?!

The trauma of being abandoned without knowing why comes flooding back. Iseul decides to team up with Baek Seol, who also hates Shinwoo. Is it revenge, or just lingering attachment? This time, who will be the one to get hurt first?