Kotaro Sakuma, Koguma Sky Blue
Full Name: Kotaro Sakuma
Ranger Designation: Koguma Sky Blue

Kotaro Sakuma is a young boy from Earth. Soon after his younger brother Jiro was born, they lost their mother Akemi to illness. He is first seen with Jiro by Lucky and the others defying Jark Matter's occupation. They are captured by Eriedrone to be used as bait to attract the Kyurangers, but Stinger, pretending to be his ally, rescues the two brothers. Kotaro reveals himself to be a spy sent by Shou and remind Stinger of his bond with his older brother Scorpio prior to the latter's betrayal and siding with Jark Matter. Inspired by Stinger, Kotaro decides to join the Rebellion. Stinger reminds him not to follow his brother's mistake. He later gains his own Change Kyutama from the spirit of Shou's predecessor, Big Bear, allowing him to transform into Koguma Sky Blue. Some time after joining, Kotaro leaves the team temporarily for training at the Rebellion HQ to become a full-fledged Kyuranger. He later returns to the team for the final battle against Scorpio and Jark Matter.