Not much is known about Dragon Fiend. He follows Matic's orders, which likely means he's a Strider, and a member of Matic's personal unit. He wears a red samurai armor and carries a japanese katana as his weapon of choice, which can throw "Plasma Arrow" projectiles like Hiryu's Cypher. This may indicate the weapon is in fact a customized Cypher, not different from Matic's personal "long" Cypher.
Dragon Fiend has been given direct orders from Matic to guard over Kuramoto's residence in Japan and eliminate anyone who comes close or attempts to see him. On his search for information about the ZAIN Project, Hiryu comes to Japan and has to face and defeat Dragon Fiend in order to see the director. Hiryu faces him again on his path to destroy the ZAIN Terminal in Africa, where Dragon Fiend is defeated a second time.
During Hiryu's infiltration of the Red Dragon, Dragon Fiend challenges Hiryu again, alongside the remains of the Strider Matic Unit. He fights him one last time and is defeated for good.
Dragon Fiend attacks with quick movements and sword strikes. His attack pattern consists of quickly running towards Hiryu, attack him once with a downward slash and then retreat in order to repeat the pattern. Every 2 or so attacks, he'll stop and attack from a distance, charging and shooting a Plasma Arrow projectile, which can be easily avoided by either jumping or ducking.
He can be attacked at any point during battle, even while he's attacking. It's best to strike at him while he's retreating or, if close enough, while charging up the Plasma Arrow.