A mischievous ghost boy named Q-Taro comes to live with the Ohara family after hatching from a mysterious egg that young Shota Ohara finds. Despite being a ghost from a place called Ghost Country, which floats on the clouds, Q-Taro is good-natured, delicate, and lovable, though he is also a scatterbrained troublemaker who loves to play pranks, scare people, and steal food. He possesses typical ghost abilities such as flying through the sky, becoming invisible, passing through walls, and talking with animals, but he has one glaring weakness: a desperate, overwhelming fear of dogs. He also lacks the ability to transform into other shapes, a skill most other ghosts possess.

The story unfolds in the everyday setting of Shota's home and neighborhood, focusing on the comedic and warmhearted troubles Q-Taro causes for the Ohara family, which includes Shota, his older brother Shinichi, and their parents. Q-Taro becomes best friends with Shota, a young schoolboy with poor grades, and joins him in his adventures and misadventures with his classmates. Their friend group includes the kind honor student Yoshiko, the genius but bald inventor named Hakase, and the school bully known as Godzilla, who is often accompanied by his henchmen Kizao, Inari, and Tanuki. The series frequently depicts Q-Taro using his powers to help Shota with problems, whether it is winning a baseball game, dealing with a neighborhood bully, or trying to overcome his own silly fears.

The narrative expands significantly with the arrival of other ghosts from Ghost Country. Q-Taro's younger sister P-ko and his baby brother O-Jiro come to live in the human world, and O-Jiro's unique speech, consisting only of the word bakeratta, becomes a popular element. Q-Taro's main rival is Doronpa, a sophisticated and arrogant American ghost who can transform and often looks down on Q-Taro, leading to many humorous and egotistical battles. Q-Taro also has a tomboyish girlfriend named U-ko, a judo expert who is stronger than he is and often uses him as a practice dummy. The series is composed of complete, self-contained stories that portray the slice-of-life interactions between the human children and their ghost friends, highlighting themes of friendship and the daily chaos of having a supernatural being in the house.

While most episodes are lighthearted comedies, the original story has a definitive and bittersweet ending. After three years of living together, Q-Taro decides he must leave the Ohara family to explore the world and learn more things on his own, feeling he cannot rely on their kindness forever. A later, more poignant conclusion shows Shota as a 25-year-old married salaryman. Q-Taro returns for a visit, but he soon realizes that his old friend now has a family and adult responsibilities, leaving no true place for a playful ghost. Feeling like an intruder and overcome with loneliness, Q-Taro quietly leaves, marking a sad but final farewell to their childhood friendship.