Matsuo lives at the Blue Sky orphanage and plays on the American football team formed by Takeshi. Their games halt when a mysterious light reveals Takeshi's alien origins, drawing Matsuo into the conflict against General Dazaan alongside fellow orphans Miki and Goro.

He pilots the "Header," the head component of the giant robot Dai Apolon. This unit transforms from a UFO saucer, one of three primary machines alongside the Trangur and Legger. Matsuo engages in combat against Dazaan's forces, supporting Takeshi during weekly battles. To form Dai Apolon, Matsuo participates in a synchronized combination sequence activated by calling "U! F! O!", which also changes his uniform.

Matsuo is distinctly associated with the color yellow, seen in his football jersey and extending to his pilot role within the team's color-coding system: Takeshi (red), Miki (pink), Goro (blue), and Hideki (white). His role involves tactical maneuvers as the Header pilot during combat and combination.

His background consistently identifies him as an orphan at Blue Sky. In the English-dubbed compilation film "Shadow World," which relocates the story to California, Matsuo's name is changed to Mark, reflecting the adaptation's Americanization of character names.