Rie Hayakawa is Kantaro Hoshi's classmate and best friend, sharing similar interests while attending the same school. Their fathers maintain a friendship, with Rie's father serving as Deputy Director Hayakawa of the International Science Police Headquarters.

Early in the series, Rie considers Kantaro physically unimpressive, teasing him relentlessly about his poor sports performance and lack of athleticism. She openly mocks him as a "weakling," unfavorably comparing him to Earth's defending giant robot Ganger and accusing Kantaro of fleeing during alien saucer attacks. Their playful arguments often involve her misinterpreting his knowledge of Ganger's capabilities as jealousy.

Due to her closeness to Kantaro, Rie frequently becomes a target for the alien Blasters. They exploit her as bait to lure him into confrontations, capitalizing on his inability to tolerate her endangerment. This establishes her recurring damsel-in-distress role.

A pivotal shift occurs when Rie uncovers Kantaro's secret identity as Ganger's pilot. The revelation humbles her, halting her mockery as she grasps the true weight of his responsibilities and courage. Her perception transforms upon realizing he risks his life piloting Ganger to protect Earth.