Following her mother's remarriage, Tooko, a 26-year-old office lady, gains a younger brother, Natsu—a boy half her age. Upon their first meeting, Tooko is immediately met with a glare, which gives her the impression that he hates her. Furthermore, as their newlywed parents wish to spend time alone every week, Natsu ends up staying over at Tooko's apartment every Wednesday, filling her with unease during each of their reunions.

After forgetting their meeting and arriving late to her apartment, Tooko panics, believing that she has further angered her brother. However, Natsu unexpectedly starts showing care for her instead, preparing dinner alongside a mocktail—a non-alcoholic cocktail. As the two drink together, they begin to put their feelings into words, revealing their shared desire to grow closer to one another. Hoping to bring this wish to fruition, the siblings start making mocktails every Wednesday, slowly forming an everlasting bond in the process.

[Written by MAL Rewrite]