Set in the Tokyo neighborhood of Sugamo, an area known for its high population of elderly residents, a pair of very young twin siblings spend their days exploring the world around them. The older sister, known simply as Onei, and her younger brother, Junichiro, are a tightly bonded pair whose parents are almost always away from home for work. As a result, the twins are effectively raised by the kindness of their mother's friends and the watchful eyes of the entire local community, who look out for them and guide their playful adventures.

Onei is the more assertive and imaginative of the two, often leading the charge into new experiences or mischief, while Junichiro is a quieter and more observant companion who follows his sister's lead. Despite their young age, the twins display a remarkable degree of independence, a cheerful curiosity about everything they encounter, and an unusually good fortune that seems to keep them out of serious trouble even when their innocent schemes go awry. Their world is one of simple, everyday wonders, from buying snacks at a local shop to making friends with neighborhood cats or chatting with the friendly elderly people who populate their streets.

The narrative is built around episodic, slice-of-life vignettes that capture the small joys and gentle humor of childhood. There is no grand, overarching conflict; instead, the story finds its heart in the quiet, resonant moments of the twins' daily life, their interactions with the colorful cast of adults around them, and the way they absorb the rhythms of their tight-knit community. A recurring thread involves the twins' parents, who remain a distant but beloved presence in their lives, occasionally sending word from their jobs abroad. A notable narrative development occurs when the twins reach their fourth birthday, prompting a move from Sugamo to the neighboring district of Yamato-go, a shift that expands their world and introduces a new set of local characters into their lives. Through every encounter, the series maintains a warm, gentle tone, emphasizing the resilience of childhood and the subtle, sustaining power of community care.