The manga Shinanonchi no Ikuru is set in Japan during the late Showa period, stretching into the early Heisei era, and is a nostalgic comedic memoir centered on the daily lives of two siblings. The story focuses on the young boy Ikuru, who is described as silly but lovable, and his older sister Shinano, who is stern and frightening when angered but deeply cares for her younger brother. The narrative depicts the laughter-filled chaos of their relationship alongside their family and friends, capturing the essence of a realistic sibling dynamic.

As the series progresses, the scope expands to include the siblings' circle of acquaintances. A notable narrative arc in later volumes introduces Ikuru’s classmate, a science-oriented girl named Sasaki. She struggles with expressing her emotions and tends to overthink situations, but through her interactions with Ikuru and another classmate named Shu, she begins to relax and open up. Other recurring characters include Ikuru’s friends, Onizuka, and Kimura-kun.

The stories are driven by the simple, relatable activities of childhood during that time period, such as visiting candy stores, collecting rare stickers, playing dodgeball, riding five-step switching bicycles, and reading Shonen Jump magazine. The series aims to evoke a sense of nostalgia for a bygone era of childhood play and simple entertainments.