Eiichi Kite, nicknamed Kiteretsu, is an 11-year-old fifth grader living in Tokyo. He demonstrates exceptional intellect and inventive genius. His fascination with mechanics stems from studying an encyclopedia created by his Edo-period inventor ancestor, Kiteretsu Saisama. This encyclopedia forms the basis for his creations, which also include modifying, repairing, and developing original variations of machines. Financially constrained, he funds his inventions only through his allowance and New Year's money. Consequently, a broken gadget remains inoperable until he saves enough for repairs. Despite his academic prowess, he struggles significantly with athletics and sports.

His most significant invention is Korosuke, a robot companion built from designs in the ancestral encyclopedia. Korosuke, who ends sentences with "nari" and wears an artificial samurai sword, serves as Kiteretsu's primary assistant and closest friend. Their relationship is defined by mutual loyalty and support during adventures.

Kiteretsu's mother, Michiko Kite, maintains strict focus on his academic studies, leading him to often conceal his inventing. In contrast, his father, Eitarou Kite, actively encourages his son's passion. His social circle includes Miyoko Nonohana, an intelligent neighborhood friend and love interest. Time travel episodes reveal Miyoko becomes his future wife; they have a son named Eitarou after Kiteretsu's father. Kaoru Kumada, nicknamed Buta Gorira, initially acts as a bully but evolves into comic relief; his family runs a vegetable shop, and he sometimes seeks Kiteretsu's help with homework or inventions. Kouji Tongari, a wealthy yet easily frightened friend, is often teased by Kaoru but remains part of their core group.

Kiteretsu frequently embarks on adventures using a self-built time machine, traveling across eras. These journeys sometimes involve interactions with his ancestor, Kiteretsu Saisama, and offer glimpses into potential future events concerning his relationships and family life.