On his way home from work one day, salaryman Yu Tanemura (5 years into corporate life) rescues his junior colleague Haru Serizawa from persistent street harassers.

What begins as an impromptu dinner together quickly reveals Haru’s true nature – while she plays the sweet, alcohol-averse “little sister” type at the office, she’s actually a sharp-tongued heavy drinker with troublesome tendencies.

Yet Yu finds himself genuinely enjoying their time together, and at Haru’s suggestion, they become regular drinking buddies. As their weekly drinking sessions continue, Haru’s sense of personal boundaries begins glitching spectacularly:

“Yu-senpai~ You’re just dying to drink with cute little me, aren’t you?”

“Ehehe~ Yu-senpaaai Yu-senpaaaai~”

“Yu-senpai, why don’t we drink at my place tonight?”

What begins as simple camaraderie gradually awakens romantic feelings in Yu, until he starts seeing her not just as a drinking partner… but as a woman.