The Fivemen are five siblings of the Hoshikawa family (three brothers and two sisters), separated from their parents during a sudden Zone attack, sent to board a ship along with Arthur G6 to be raised and learn of the Fiveman technology. They pose as teachers at New Town School, planting a garden of Sidon Flowers which they brought from planet Sidon.
In 1970, Doctor Hoshikawa was researching how to transform the planet Sedon into a green, lush world, and tested his research by attempting to grow flowers. On the day the first flower bloomed, the Zone Empire launched an assault on the planet, he and his wife were separated from their five children. Arthur G6 took the five children back to Earth and raised them. 20 years later, the five are now teachers in the same school. The Zone empire now prepares to invade Earth as its thousandth target and as they begin the attack, three vehicles appear and counter the offensive. Five warriors descend from the vehicles and confront Zone. The Hoshikawa siblings have been developing the Fiveman technology and training hard in case Zone attempts to invade Earth. Now, the five siblings are ready to battle with the familiar foes as Fiveman. After defeating the Zone Empire, the Fivemen departed Earth to recover their stranded parents.