From Wikifang, a definitive guide to Telefang, Dino Device and BugsiteShigeki who appears in both Keitai Denjuu Telefang: Speed and Keitai Denjuu Telefang: Power.
He is something of a child genius, and deeply interested in the Denjuu World, which he had never visited before. After he and Shigeki accidentally arrive there via the D-Shot that Shigeki picked up, Matsukiyo stays with Musa in Toronko Village and gives Shigeki advice during the course of the story.
In Telefang 2, Matsukiyo appears as a professor living in the Human World. He offers rewards through the D-Shot's Wanted application, in exchange for information on specific Denjuu.
 In the manga
 Telefang 1
In the Telefang 1 manga, Matsukiyo takes a much more active role than in the games, exploring the Denjuu World with Shigeki. He befriends a Waratah in Toronko Village, which becomes his partner Denjuu. There are also a series of 4-koma featuring Matsukiyo in volume 3 of the collected set.
 Telefang 2
Matsukiyo also appears in the Telefang 2 manga.