A second year high school student and Rin's childhood friend. He is the one who taught Rin in making paper planes. Kei and Rin are in different classes and Rin usually go to Kei's classroom to throw a paper plane on him with message.He became friends with Ryuusuke who was Rin's classmate and also became friends with Aoi who was Kei's classmate. Kei seems to like Rin, though he's somewhat oblivious to his own feelings.He forgot how to make paper planes but Rin taught him. He loves paper planes.