The Niji no Hebi (lit. "Rainbow Serpent") are a criminal ninja clan serving as the main antagonists of the Rider Time Shinobi special.
Niji no Hebi were the ones behind the passing of the "Diet" act in Japan, which compelled all citizens of Japan to learn how to use ninjitsu to manipulate the elements.
The Niji no Hebi began hunting Iroha Kagura, the princess of their clan, while she was doing an obstacle course to determine her ninja skills. However, they are driven off by Iroha's brother, Rentaro Kagura / Kamen Rider Shinobi. The Niji no Hebi later target Iroha again after she advances to the finals of the tournament. In the final round, a ninja variation of Capture the Flag, the referee for the tournament (who is secretly a member of the Niji no Hebi) announces a special rule for the tournament where if one ninja kills all the others that ninja will win. The Niji no Hebi also insert four Stardust Ninja Dustards to be Iroha's competitor in the tournament. However, Shinobi interrupts the tournament and defeats the four Dustards to save his sister.
Later on though, Yaminin figures out that Kagura is Shinobi and manages to restrain Kagura by creating a giant snake and having it wrap around him.