Rai Kotaru (雷甲太郎?), often nicknamed Raikou Rai Kōtarō (ライコウ?) is a fictional Japanese reporter and motorcyclist, as well as the deuteragonist of Toho's 1973 tokusatsu television program, Warrior of Light Diamond Eye.
Rai Kotaru is a reporter for the "Weekly Japan" and an avid motorcyclist, favoring his bike Thunder Number. Pressured by his superior Gozo Osawayama, Rai finds himself on the trail of a gang of repeated gem thieves. He follows a lead to gem trader Gen Kai Ryu, but soon realizes that Gen Kai Ryu is actually the leader of the gem thieving gang. Gen Kai Ryu restrains Rai with rope and prepares to execute him when suddenly one of the stolen jewels, the "King of Arabia", begins to glow and a voice from it orders Gen to stop. Suddenly, a blue diamond-clad figure appears from the gem and introduces himself as Diamond Eye. He breaks Rai's bonds and chases the gangsters to a field. There, the hero hits the men with twin beams from his eyes which reverts them into their true forms: ancient beasts known collectively as the Zensei Majin. As Raikou watches from the sidelines, Diamond Eye combats the Zensei Majin before him whom include Mojingah, multiple Cow and Horse People, and Gen Kai Ryu who was transformed into King Cobra. Ultimately, Mojingah and the Cow and Horse People are defeated at the hands of Diamond Eye, but King Cobra manages to escape with his female accomplice Shu Dama. Once the chaos is fully subsided, Diamond Eye equips Raikou with a diamond ring, inside of which Diamond Eye resides, and with it he can call forth the hero when necessary.