Ken and Ginjiro Mizuno are a pair of brothers who were chosen to become the Byclossers to defend the world from the evil Dester organization and the titular main protagonists of Kyodai Ken Byclosser.
Ken is portrayed by Tetsu Kaneko and Ginjiro is portrayed by Yuki Tsuchiya.
Ken and Ginjiro were born on January 1st, 1965 at 1:01 am and February 2nd, 1968 at 2:02 am respectively, leading them to be selected by Pegasus, the guardian deity of Hydra in the third galactic system, to become the Byclossers to defend the world from evil.
When Ken reached adulthood and Ginjiro was in high school, the Dester organization emerged to terrorize children in order to please the idol Majin Gola so it would reward them with riches. While riding to Okutuma on their motocycles one day, the two brothers ran into agents of the Dester organization led by Dester's Lady Commander Sylvia. The two were attacked by Dester's Blackmen combatants, but were saved by a mysterious glowing orb of energy. The orb introduced itself as the guardian deity of the Hydra system and revealed the two brothers had been selected to become the guardians of the planet to face the evil that was coming, bestowing upon them the power to transform into Byclosser Ken and Byclosser Gin to fight evil.
After returning home the two brothers discovered telepathically that their friend Akemi Takeda was being terrorized by Dester and went to go save her. Becoming Byclossers Ken and Gin, the two brothers defeated the Dester Robot Onigan and saved Akemi, bringing her home safely.