Senpai no Sodatekata

Karino receives a confession from Kusaka, a junior member of his film club. Despite Karino repeatedly telling him, "I'm the last guy you should go for," Kusaka was the cutest junior—and he refused to give up on expressing his feelings. On the night their feelings finally align, it turns out Karino has a secret trait that manifests while they're having sex...?

(Source: Tokyo Mangasha, translated)