Chitose Oki has been in love with his nextdoor neighbor Tomo since childhood. When they were young, Chitose declared he would marry her once he grew up, and Tomo agreed on one condition: he must become taller than her. Unfortunately, Chitose took this promise far more literally than intended. Years later, Chitose remains frustratingly short while Tomo has only grown taller, leaving him convinced he is still unworthy of confessing. The central irony driving the story is that the two have completely different interpretations of the height requirement. Chitose believes he must physically surpass Tomo's full adult stature, a goal that seems increasingly impossible. Tomo, however, remembers their childhood pact differently, she only meant that he needed to grow taller than she was on the day they made the promise, a bar he likely cleared long ago without realizing it. Neither is aware of the other's misunderstanding, so they remain locked in a stalemate of unspoken affection, each waiting for a condition only one of them knows has already been met.

The story unfolds in a quiet Japanese suburban neighborhood where Chitose and Tomo live as neighbors. Chitose is a criminally optimistic high schooler who radiates positive energy, but his singular focus on increasing his height leads him into all sorts of comedic schemes. Convinced that growing taller is the only path to Tomo's heart, he tries everything from drinking milk to specific exercises, all while remaining completely oblivious to the fact that Tomo already treats him with a warmth and care she shows no one else. Tomo is a kind-hearted upperclassman admired by everyone around her for her gentle and thoughtful nature. She watches over Chitose with undisguised fondness, but her own shyness and her belief that he simply needs to reach a height he has already achieved prevent her from simply telling him the truth.

Daily life provides the backdrop for a series of embarrassing misunderstandings and sweetly awkward encounters. A classic rainy day umbrella scene takes on new life when Tomo is the one holding it over Chitose. When heavy boxes need moving, Tomo effortlessly lifts them while Chitose strains at the weight. Their friends watch this dance of mutual obliviousness with a mixture of amusement and exasperation, occasionally trying to nudge the pair toward clarity. One friend even explains to Chitose that Tomo does not treat him like a little brother so much as she mothers him, a distinction that goes completely over his head. Tomo's older brothers also appear periodically to add chaos and commentary, their teasing often pushing the two leads into even more awkward but endearing situations.

The manga unfolds in short, episodic chapters, each only a few pages long, giving the story the intimate feel of glimpsing small but meaningful moments in the characters' lives rather than following a fast-paced plot. Chitose continues obsessing over every millimeter of growth, measuring himself constantly and celebrating any tiny increase that brings him closer to his imagined goal. Meanwhile, Tomo quietly waits, already certain that he has long since met her condition, but too hesitant to propose herself or reveal the true terms of the old promise. The supporting cast, including a pair of side characters who gradually develop their own relationship through a shared love of a particular author, provide additional warmth and comic relief. Their romantic progress often highlights just how stuck Chitose and Tomo remain, as side couples manage to confess while the main pair cannot even acknowledge they like each other.

Throughout the narrative, the comedy never comes at Chitose's expense. His narrow view of manhood and his obsession with height could easily be played for cruel jokes, but the manga instead treats his earnestness with genuine affection. The humor arises from the gap between his elaborate efforts and the simple truth he cannot see, combined with Tomo's equally stubborn refusal to clarify the misunderstanding. Both characters clearly adore each other, and their interactions, whether Chitose struggling to reach a high shelf or Tomo blushing at his enthusiasm, are consistently warm and wholesome. The story builds toward the inevitable moment when the truth about their competing interpretations must finally surface, leading to the confession both have been waiting for since childhood, though only one knew the waiting was already over.