In the manga, Kurogane Yaiba is a skilled samurai but lacks knowledge in other areas. He and his father, Kenjurou, live in a forest and, one day, they are attacked by a group of gorillas during a meal. They hide in a box of pineapples meant for transportation to the city, where Yaiba discovers he is a renowned warrior and must face off against Takeshi, a high school student with a demonic appearance.
Throughout his journey to become a true samurai, Yaiba is motivated, trained, and inspired by various people. Despite his sword skills and kindness, he retains a childish nature and can be impulsive. He loses allies due to his stubbornness, but with the help of his friends, he overcomes challenges. The group goes on many adventures and meets historical figures, facing otherworldly threats to save the planet.
Overall, the manga showcases themes of love, friendship, perseverance, and determination.