In their final year of high school, ace pitcher Minami Makoto is haunted by the memory of a promise. Years ago, his childhood best friend and former battery partner, Wajima Shuusuke, suddenly moved away, leaving Makoto with the words, "Let's meet at Koshien." Makoto has clung to that pledge ever since, channeling his longing into baseball. Now, he is the star pitcher of his school's team, forming a formidable new battery with the reliable and fiercely devoted team captain, Shiratori Hokuto. Makoto tells himself that as long as he keeps playing, he will eventually see Shuusuke again.

That fragile hope is shattered and reignited when, in the spring of their third year, Shuusuke suddenly transfers back to their school. But the boy who returns is not the same catcher Makoto remembers. He is distant, claims he has quit baseball, and his sudden reappearance throws Makoto's world into turmoil. Hokuto, who has quietly fallen for Makoto, watches the tension between the two former partners with a growing sense of unease and his own hidden feelings.

What follows is a bittersweet and intensely emotional love triangle set against the backdrop of the boys' final summer of high school. Makoto is torn between his lingering, years-long crush on Shuusuke and the steady, patient affection of Hokuto, who has always been by his side. Shuusuke, grappling with his own past trauma and a confession of his own to make, slowly begins to recognize his feelings. As the summer baseball tournament approaches, the three boys must confront their unresolved histories, navigate the heat of competition, and decide where their hearts truly lie, all while knowing that this season of youth is fleeting.