Unmeiteki Lovemeter

Kai Shizuki is an ex-idol who is considered a prince at school, but he has a secret. He can see balloons above people's heads that give away their true emotions toward him. One day, while being chased by fans, Shizuki is unexpectedly saved by Shinozuka, the supposed bad boy. Even more surprising, Shinozuka's balloons are bigger and glossier than any Shizuki has ever seen before.

(Source: Kaiohsha, translated)