In the late 1950s, during the Showa era, a young hero known as Shounen Dash roamed Tokyo in his gadget-laden car, the Dash-go, solving crimes with the help of his assistant Fumie, the sympathetic Wakana police chief, and reporter Nagata. His arch‑nemesis, Dokuro-hakase (Skull Doctor), eventually lured him into a flash‑freezing device, sealing him in ice. Decades later, in the early 2000s, high school student Yokoyama Hikari discovers the frozen boy in the basement of her grandfather’s former detective agency. The device releases him upon sensing her presence, and Hikari learns that the boy is actually her grandfather—Fumie’s son, making him the man who would become the grandfather she never knew.

This surreal situation forces a modern teenage girl and a juvenile detective from the Showa era to share a home. Dash, still thinking and acting like a 1950s hero, brings his outrageous sense of justice, a car that can fly and fire missiles, and an arsenal of gadgets into 21st‑century Tokyo. Hikari is repeatedly caught up in his antics, often to her embarrassment and exasperation. The series balances slapstick comedy and culture‑clash humor with occasional heartfelt stories about family bonds across generations.

Over the course of the manga, the cast expands to include Hikari’s friends, her mother, and a recurring rival or ally in the form of a female spy. The early volumes depict standalone episodes pitting Dash against modern‑day criminals, haunted museums, and even a water‑bikini contest. A major narrative arc, Toki o Kakeru Ponytail, begins when Dash (now aware of his situation) invents a time‑travel device. Hikari accidentally gets sent back to the 1950s, where she becomes a hostage in a foreign incident and is rescued by the younger, still‑active Dash. The resulting timeline confusion leads to a confrontation between the Showa‑era Dash and the time‑traveling Dash from the future, and the conflict ultimately reveals the secret of Dash’s birth and identity.

The story concludes with Dash and Hikari resolving the time‑travel paradox, and a final chapter that brings the family circle to a warm close. Throughout its five volumes, the manga parodies classic boy‑detective tales, features generous ecchi and action elements, and uses the generation‑gap premise to explore how heroism and innocence can survive across decades.