Mariko "Mari" Kumakura has always been an excellent student, but because of her quiet and timid demeanor, she has always been isolated from her peers. However, the outgoing and popular Akiko "Akko" Oohashi plans to change that by becoming Mari's best friend through her constant optimism and persistence. The two, along with Akko's other friends—the carefree Satoko Sugiyama and energetic Tamami Sekine—deal with the troubles of school and everyday life for teenage girls, discovering just how difficult growing up can be.

As they spend more and more time together, Mari and Akko's affection for each other grows. Beginning to wonder if friends are supposed to feel this way, how will this affect their budding relationship?