Kouta Matsushiro has a crush on a classmate who barely warms to anyone, and a self-proclaimed angel named Sasara decides to fix that for him. She marks a counter on his arm that ticks down from ten every time his heart jumps near the girl, and at zero he says out loud whatever he happens to be thinking. Every power Sasara has runs on the number ten, from stopping time to reading who likes whom, and Kouta's quiet feelings turn into a running disaster.