The story follows (also called Yuuki in some translations), a young boy living with his older sister, Reiko, after their parents passed away.
The story takes place in the summer of 1986, during the Japan-Soviet diplomatic relations. The series revolves around Takeo, who has never experienced a normal adolescence due to his frail health. He and his grandmother move to the countryside for the summer. There, he confesses to a girl named Naoki but there appears a rift turning events quite on various , more dramatic mood related .
The series has sparked discussions on social media platforms like TikTok and Facebook regarding its production quality and the specific "summer heat" atmosphere it portrays.
One of the primary themes of "Shounen ga Otona ni Natta Natsu" is the transition from adolescence to adulthood. Masamune's journey serves as a metaphor for the struggles and challenges that young people face as they navigate the complexities of growing up. Through his relationships with Saichi, Aya, and other characters, Masamune learns valuable lessons about friendship, love, and the importance of taking responsibility for one's actions.